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weekly contest 307
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‎README.md‎

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@@ -4,6 +4,7 @@ Record leetcode contest and ideas every week, and encourage yourself to think mo
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leetcode url: <https://leetcode.cn/u/cctest/>
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* 🐻 [weekly contest 307](src/main/java/weekly/wk307.java) 贪心 | 贪心 | 图 | 堆
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* 🐻 [weekly contest 306](src/main/java/weekly/wk306.java) 数组 | 有向图图 | 贪心、栈 | 数位DP
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* 🐨 [weekly contest 305](src/main/java/weekly/wk305.java) Array | Array | DP | DP
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* 🐍 [weekly contest 304](src/main/java/weekly/wk304.java) Array | Array Greedy | Graph | Graph Topological Sort
@@ -23,6 +24,7 @@ leetcode url: <https://leetcode.cn/u/cctest/>
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* 🐶 [weekly contest 290](src/main/java/weekly/wk290.java)
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* 🐭 [weekly contest 280](src/main/java/weekly/wk289.java)
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* 🐹 [biweekly contest 85](src/main/java/weekly/wkb85.java) 滑动窗口 | 模拟 | 差分数组 | 并查集
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* 🐹 [biweekly contest 82](src/main/java/weekly/wkb82.java) DFS | Greedy | Greedy| Monotonic Stack/Union Find
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* 🐹 [biweekly contest 81](src/main/java/weekly/wkb81.java)
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* 🐰 [biweekly contest 80](src/main/java/weekly/wkb80.java)

‎src/main/java/weekly/wk307.java‎

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package weekly;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.HashMap;
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import java.util.HashSet;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.Map;
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import java.util.PriorityQueue;
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import java.util.Queue;
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import java.util.Set;
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public class wk307 {
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//ranking: 659 / 7064
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//简单题，注意比赛顺序是从后往前的..
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public int minNumberOfHours(int initialEnergy, int initialExperience, int[] energy, int[] experience) {
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int ans = 0;
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for (int i = 0; i < energy.length; i++) {
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if (energy[i] >= initialEnergy) {
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//严格大于
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ans += energy[i] - initialEnergy + 1;
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initialEnergy += energy[i] - initialEnergy + 1;
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}
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//精力扣除
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initialEnergy -= energy[i];
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if (experience[i] >= initialExperience) {
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//严格大于
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ans += experience[i] - initialExperience + 1;
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initialExperience += experience[i] - initialExperience + 1;
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}
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//经验上涨
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initialExperience += experience[i];
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}
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return ans;
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}
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//中等题，注意边界条件，只需计算前半部分即可
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public String largestPalindromic(String num) {
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int[] count = new int[10];
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for (char c : num.toCharArray()) {
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count[c - '0']++;
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}
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StringBuilder sb = new StringBuilder();
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for (int i = count.length - 1; i >= 0; i--) {
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while (count[i] >= 2) {
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sb.append(i);
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count[i] -= 2;
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}
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}
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boolean add = false;
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int c = -1;
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for (int i = count.length - 1; i >= 0; i--) {
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if (count[i] > 0) {
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add = true;
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c = i;
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break;
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}
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}
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//
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while (sb.length() > 0 && sb.charAt(0) == '0') {
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sb.delete(0, 1);
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}
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//没有单独的>0的数字
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if (c <= 0 && sb.length() == 0) return "0";
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StringBuilder reverse = new StringBuilder(sb).reverse();
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if (!add) {
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return sb.append(reverse).toString();
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} else {
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return sb.append(c).append(reverse).toString();
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}
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}
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public class TreeNode {
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int val;
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TreeNode left;
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TreeNode right;
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TreeNode() {
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}
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TreeNode(int val) {
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this.val = val;
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}
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TreeNode(int val, TreeNode left, TreeNode right) {
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this.val = val;
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this.left = left;
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this.right = right;
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}
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}
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//中等题，先计算图，然后bfs
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public int amountOfTime(TreeNode root, int start) {
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Map<Integer, List<Integer>> map = new HashMap<>();
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help(root, map, -1);
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Queue<Integer> queue = new LinkedList<>();
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queue.add(start);
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Set<Integer> set = new HashSet<>();
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int time = 0;
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set.add(start);
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while (!queue.isEmpty()) {
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int size = queue.size();
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while (size-- > 0) {
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Integer poll = queue.poll();
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if (!map.containsKey(poll)) continue;
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for (Integer next : map.get(poll)) {
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if (set.contains(next)) continue;
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set.add(next);
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queue.add(next);
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}
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}
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time++;
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}
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return time - 1;
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}
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void help(TreeNode root, Map<Integer, List<Integer>> map, int up) {
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if (!map.containsKey(root)) {
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map.put(root.val, new ArrayList<>());
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}
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if (up != -1) {
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map.get(root.val).add(up);
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}
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if (root.left != null) {
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map.get(root.val).add(root.left.val);
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help(root.left, map, root.val);
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}
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if (root.right != null) {
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map.get(root.val).add(root.right.val);
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help(root.right, map, root.val);
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}
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}
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class Pair {
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long sum = 0;
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int index = 0;
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Pair(long sum, int index) {
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this.sum = sum;
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this.index = index;
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}
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}
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//困难题，当时没想出来，看了题解恍然大悟
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public long kSum(int[] nums, int k) {
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//最大的数一定是所有正数的和
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long sum = 0;
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for (int i = 0; i < nums.length; i++) {
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if (nums[i] > 0) {
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sum += nums[i];
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} else {
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//变成正数，一律按减法处理
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nums[i] =-nums[i];
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}
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}
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if (k == 1) return sum;
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Arrays.sort(nums);
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PriorityQueue<Pair> priorityQueue = new PriorityQueue<>((a, b) -> (int) (b.sum - a.sum));
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priorityQueue.add(new Pair(sum - nums[0], 0));
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//依次对每个位置取或者不取
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for(int i=2;i<k;i++){
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Pair poll = priorityQueue.poll();
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//System.out.println(poll.sum);
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if (poll.index < nums.length-1) {
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priorityQueue.add(new Pair(poll.sum - nums[poll.index + 1], poll.index + 1));
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priorityQueue.add(new Pair(poll.sum + nums[poll.index]- nums[poll.index + 1], poll.index + 1));
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}
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}
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return priorityQueue.poll().sum;
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}
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public static void main(String[] args) {
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}
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}

‎src/main/java/weekly/wkb85.java‎

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package weekly;
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import java.util.TreeMap;
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public class wkb85 {
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//ranking: 228 / 4193
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//简单题，暴力
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/* public int minimumRecolors(String blocks, int k) {
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int ans = Integer.MAX_VALUE;
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for (int i = 0; i + k <= blocks.length(); i++) {
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int count = 0;
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for (int j = i; j < i + k; j++) {
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char c = blocks.charAt(j);
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if (c == 'W') {
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count++;
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}
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}
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ans = Math.min(count, ans);
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}
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return ans;
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}*/
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//简单题，滑动窗口
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public int minimumRecolors(String blocks, int k) {
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int ans = Integer.MAX_VALUE;
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int count = 0;
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for (int i = 0; i < k-1; i++) {
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if(blocks.charAt(i)=='W'){
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count++;
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}
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}
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for(int i=k-1;i<blocks.length();i++){
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if(blocks.charAt(i)=='W'){
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count++;
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}
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ans=Math.min(ans,count);
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if(blocks.charAt(i-k+1)=='W'){
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count--;
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}
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}
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return ans;
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}
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//中等题，暴力
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/* public int secondsToRemoveOccurrences(String s) {
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char[] chars = s.toCharArray();
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int ans = 0;
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while (true) {
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boolean change = false;
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for (int i = 1; i < s.length(); i++) {
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if (chars[i - 1] == '0' && chars[i] == '1') {
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chars[i - 1] = '1';
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chars[i] = '0';
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change = true;
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i++;
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}
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}
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if (change) ans++;
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else return ans;
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}
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}*/
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public int secondsToRemoveOccurrences(String s) {
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int res=0;
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int count=0;
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for (char c : s.toCharArray()) {
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if(c=='0'){
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count++;
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}else if(count>0){
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res=Math.max(res+1,count);
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}
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}
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return res;
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}
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public String shiftingLetters(String s, int[][] shifts) {
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char[] chars = s.toCharArray();
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//差分数组统计移动的位数
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int[] count = new int[s.length() + 1];
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for (int i = 0; i < shifts.length; i++) {
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int left = shifts[i][0];
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int right = shifts[i][1];
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int u = shifts[i][2];
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if (u == 0) {
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count[left] -= 1;
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count[right + 1] += 1;
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} else {
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count[left] += 1;
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count[right + 1] -= 1;
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}
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}
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int cur = 0;
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for (int i = 0; i < chars.length; i++) {
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cur += count[i];
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//System.out.println(chars[i] + " " + cur);
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//去除多余的循环
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chars[i] += (cur % 26);
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//+26或-26
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if (chars[i] < 'a') {
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chars[i] += 26;
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} else if (chars[i] > 'z') {
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chars[i] -= 26;
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}
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}
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return new String(chars);
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}
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//困难题，倒着思考，然后并查集合并区间
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public long[] maximumSegmentSum(int[] nums, int[] removeQueries) {
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long[] res = new long[nums.length];
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long max = 0;
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long[] sum = new long[nums.length];//用来存以i为uf key的子数组和
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UnionFind uf = new UnionFind(nums.length);
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for (int i = nums.length - 1; i >= 0; i--) {
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res[i] = max;
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int index = removeQueries[i];
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int num = nums[index];
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sum[index] = num;
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max = Math.max(max, sum[index]);
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//左边可以合并
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if (index - 1 >= 0 && sum[index - 1] > 0) {
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long s = sum[uf.find(index - 1)] + sum[uf.find(index)];
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uf.union(index - 1, index);
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sum[uf.find(index)] = s;
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max = Math.max(s, max);
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}
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//右边可以合并
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if (index + 1 < nums.length && sum[index + 1] > 0) {
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long s = sum[uf.find(index + 1)] + sum[uf.find(index)];
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uf.union(index + 1, index);
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sum[uf.find(index)] = s;
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max = Math.max(s, max);
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}
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}
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return res;
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}
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//并查集
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class UnionFind {
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public final int[] parents;
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public int count;
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public UnionFind(int n) {
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this.parents = new int[n];
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reset();
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}
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public void reset() {
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for (int i = 0; i < parents.length; i++) {
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parents[i] = i;
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}
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count = parents.length - 1;
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}
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public int find(int i) {
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int parent = parents[i];
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if (parent == i) {
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return i;
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} else {
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int root = find(parent);
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parents[i] = root;
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return root;
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}
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}
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public boolean union(int i, int j) {
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int r1 = find(i);
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int r2 = find(j);
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if (r1 != r2) {
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count--;
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parents[r1] = r2;
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return true;
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} else {
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return false;
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}
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}
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/* void isolate(int x) {
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if (x != parents[x]) {
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parents[x] = x;
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count++;
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}
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}*/
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}
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public static void main(String[] args) {
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}
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}

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