weekly contest 401

Author: ZLBer

README.md

@@ -4,6 +4,8 @@ Record leetcode contest and ideas every week, and encourage yourself to think mo
 
 leetcode url: <https://leetcode.cn/u/cctest/>
 
+
+* 🐼 [weekly contest 401](src/main/java/weekly/wk401.java)     暴力 | 前缀和 | 0-1背包 | bitset
 * 🐼 [weekly contest 400](src/main/java/weekly/wk400.java)     遍历 | 排序 | 栈 | and性质
 * 🐼 [weekly contest 399](src/main/java/weekly/wk399.java)     哈希 | 遍历 | 哈希 | 线段树
 * 🐼 [weekly contest 398](src/main/java/weekly/wk398.java)     遍历 | 前缀和 | 遍历 | 记忆化搜索/组合数

src/main/java/weekly/wk401.java

@@ -0,0 +1,118 @@
+package weekly;
+
+import java.math.BigInteger;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+
+public class wk401 {
+
+
+    //暴力
+    static public int numberOfChild(int n, int k) {
+        int d = (k % (2 * n - 2));
+        if (d < n) {
+            return d;
+        } else {
+            return n - (d - n) - 2;
+        }
+    }
+
+
+    // 前缀和
+    static public int valueAfterKSeconds(int n, int k) {
+        int mod = (int) 1e9 + 7;
+
+        long[] pre = new long[n + 1];
+        Arrays.fill(pre, 1);
+        pre[0] = 0;
+        for (int j = 0; j < k; j++) {
+            for (int i = 1; i < pre.length; i++) {
+                pre[i] += pre[i - 1];
+                pre[i] %= mod;
+            }
+        }
+
+
+        return (int) (pre[n] % mod);
+    }
+
+
+    // 0-1背包
+   /* public int maxTotalReward(int[] rewardValues) {
+        Arrays.sort(rewardValues);
+        memo = new int[rewardValues.length][2000 * 2000 + 1];
+
+        int ans = dfs(0, 0, rewardValues);
+        return ans;
+    }
+
+
+    int[][] memo;
+
+    int dfs(int x, int i, int[] rewardValues) {
+        if (i >= rewardValues.length) {
+            return x;
+        }
+        if (memo[i][x] != 0) return memo[i][x];
+        int ans = 0;
+        if (x < rewardValues[i]) {
+            ans = Math.max(ans, dfs(x + rewardValues[i], i + 1, rewardValues));
+        }
+        int jump = Math.max(i + 1, lowerBound(rewardValues, x + 1));
+        ans = Math.max(dfs(x, jump, rewardValues), ans);
+        memo[i][x] = ans;
+        return ans;
+    }
+
+    // lowerBound 返回最小的满足 nums[i] >= target 的 i
+    // 如果数组为空，或者所有数都 < target，则返回 nums.length
+    // 要求 nums 是非递减的，即 nums[i] <= nums[i + 1]
+
+    // 闭区间写法
+    private int lowerBound(int[] nums, int target) {
+        int left = 0, right = nums.length - 1; // 闭区间 [left, right]
+        while (left <= right) { // 区间不为空
+            // 循环不变量：
+            // nums[left-1] < target
+            // nums[right+1] >= target
+            int mid = left + (right - left) / 2;
+            if (nums[mid] < target)
+                left = mid + 1; // 范围缩小到 [mid+1, right]
+            else
+                right = mid - 1; // 范围缩小到 [left, mid-1]
+        }
+        return left; // 或者 right+1
+    }*/
+
+    public static void main(String[] args) {
+        wk401 w = new wk401();
+        w.maxTotalReward(new int[]{1, 1, 3, 3});
+    }
+
+
+
+    // bitset +剪枝
+    public int maxTotalReward(int[] rewardValues) {
+        int m = 0;
+        for (int v : rewardValues) {
+            m = Math.max(m, v);
+        }
+        for (int v : rewardValues) {
+            if (v == m - 1) {
+                return m * 2 - 1;
+            }
+        }
+
+        BigInteger f = BigInteger.ONE;
+        for (int v : Arrays.stream(rewardValues).distinct().sorted().toArray()) {
+            BigInteger mask = BigInteger.ONE.shiftLeft(v).subtract(BigInteger.ONE);
+            f = f.or(f.and(mask).shiftLeft(v));
+        }
+        return f.bitLength() - 1;
+    }
+
+
+
+
+}