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| 1 | +package weekly; |
| 2 | + |
| 3 | +import java.util.ArrayList; |
| 4 | +import java.util.Arrays; |
| 5 | +import java.util.Collections; |
| 6 | +import java.util.Comparator; |
| 7 | +import java.util.HashMap; |
| 8 | +import java.util.HashSet; |
| 9 | +import java.util.List; |
| 10 | +import java.util.Map; |
| 11 | +import java.util.Set; |
| 12 | +import java.util.TreeMap; |
| 13 | + |
| 14 | +public class wkb113 { |
| 15 | + |
| 16 | + //找到截断点 |
| 17 | + public int minimumRightShifts(List<Integer> nums) { |
| 18 | + if (nums.size() == 1) return 0; |
| 19 | + List<Integer> list = new ArrayList<>(); |
| 20 | + if (nums.get(0) < nums.get(nums.size() - 1)) { |
| 21 | + list.add(0); |
| 22 | + } |
| 23 | + for (int i = 1; i < nums.size(); i++) { |
| 24 | + if (nums.get(i) < nums.get(i - 1)) { |
| 25 | + list.add(i); |
| 26 | + } |
| 27 | + } |
| 28 | + if (list.size() > 1) return -1; |
| 29 | + |
| 30 | + return (nums.size() - list.get(0)) % nums.size(); |
| 31 | + |
| 32 | + } |
| 33 | + |
| 34 | + //贪心 |
| 35 | + static public int minLengthAfterRemovals(List<Integer> nums) { |
| 36 | + |
| 37 | + List<Integer> list = new ArrayList<>(); |
| 38 | + int count = 1; |
| 39 | + for (int i = 1; i < nums.size(); i++) { |
| 40 | + if (nums.get(i).equals(nums.get(i - 1))) { |
| 41 | + count++; |
| 42 | + } else { |
| 43 | + list.add(count); |
| 44 | + count = 1; |
| 45 | + } |
| 46 | + } |
| 47 | + list.add(count); |
| 48 | + if (list.size() == 1) return nums.size(); |
| 49 | + Collections.sort(list, Comparator.reverseOrder()); |
| 50 | + |
| 51 | + int max = list.get(0); |
| 52 | + int left = 0; |
| 53 | + for (Integer integer : list) { |
| 54 | + left += integer; |
| 55 | + } |
| 56 | + left -= max; |
| 57 | + return max >= left ? max - left : nums.size() % 2; |
| 58 | + } |
| 59 | + |
| 60 | + |
| 61 | + // 哈希 |
| 62 | + static public int countPairs(List<List<Integer>> coordinates, int k) { |
| 63 | + |
| 64 | + int ans = 0; |
| 65 | + Map<String, Integer> map = new HashMap<>(); |
| 66 | + for (int i = 0; i < coordinates.size(); i++) { |
| 67 | + int x = coordinates.get(i).get(0); |
| 68 | + int y = coordinates.get(i).get(1); |
| 69 | + for (int j = 0; j <= k; j++) { |
| 70 | + int cx = x ^ j; |
| 71 | + int cy = y ^ (k - j); |
| 72 | + |
| 73 | + ans += map.getOrDefault(cx + "-" + cy, 0); |
| 74 | + } |
| 75 | + |
| 76 | + map.put(x + "-" + y, map.getOrDefault(x + "-" + y, 0) + 1); |
| 77 | + } |
| 78 | + return ans; |
| 79 | + } |
| 80 | + |
| 81 | + |
| 82 | + //换根dp |
| 83 | + public int[] minEdgeReversals(int n, int[][] edges) { |
| 84 | + Map<Integer, List<int[]>> map = new HashMap<>(); |
| 85 | + for (int[] edge : edges) { |
| 86 | + if (!map.containsKey(edge[0])) { |
| 87 | + map.put(edge[0], new ArrayList<>()); |
| 88 | + } |
| 89 | + if (!map.containsKey(edge[1])) { |
| 90 | + map.put(edge[1], new ArrayList<>()); |
| 91 | + } |
| 92 | + map.get(edge[0]).add(new int[]{edge[1], 0}); |
| 93 | + map.get(edge[1]).add(new int[]{edge[0], 1}); |
| 94 | + } |
| 95 | + |
| 96 | + //计算正反路径次数 |
| 97 | + int[] count = dfs(0, -1, map); |
| 98 | + |
| 99 | + int[] ans = new int[n]; |
| 100 | + // |
| 101 | + help(0, -1, map, count, new int[2], ans); |
| 102 | + return ans; |
| 103 | + } |
| 104 | + |
| 105 | + |
| 106 | + int[] dfs(int cur, int pre, Map<Integer, List<int[]>> map) { |
| 107 | + int[] ans = new int[2]; |
| 108 | + for (int[] next : map.get(cur)) { |
| 109 | + if (next[0] == pre) continue; |
| 110 | + ans[next[1]]++; |
| 111 | + int[] child = dfs(next[0], cur, map); |
| 112 | + ans[0] += child[0]; |
| 113 | + ans[1] += child[1]; |
| 114 | + } |
| 115 | + return ans; |
| 116 | + } |
| 117 | + |
| 118 | + // |
| 119 | + |
| 120 | + void help(int cur, int pre, Map<Integer, List<int[]>> map, int[] count, int[] parent, int[] ans) { |
| 121 | + |
| 122 | + |
| 123 | + //根节点的反路径-根节点到此的反路径+根节点到此的正路径 |
| 124 | + ans[cur] = count[1] - parent[1]+parent[0]; |
| 125 | + |
| 126 | + for (int[] next : map.get(cur)) { |
| 127 | + if (next[0] == pre) continue; |
| 128 | + parent[next[1]]++; |
| 129 | + help(next[0], cur, map, count, parent,ans); |
| 130 | + //回溯 |
| 131 | + parent[next[1]]--; |
| 132 | + } |
| 133 | + } |
| 134 | + |
| 135 | + |
| 136 | + public static void main(String[] args) { |
| 137 | + minLengthAfterRemovals(Arrays.asList(1000000000, 1000000000)); |
| 138 | + } |
| 139 | +} |
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