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LC.P2583[二叉树中的第K大层和] 方法一：BFS+排序123456789101112131415161718192021222324252627282930313233343536/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */class Solution { ...

LC.P889[根据前序和后序遍历构造二叉树] 方法一：DFS+哈希表123456789101112131415161718192021222324252627282930313233343536373839/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */class Soluti ...

LC.P106[从中序与后序遍历序列构造二叉树] 方法一：DFS+哈希表12345678910111213141516171819202122232425262728293031323334353637383940/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */class Sol ...

LC.P105[从前序与中序遍历序列构造二叉树] 方法一：DFS+哈希表12345678910111213141516171819202122232425262728293031323334353637383940/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */class Sol ...

LC.P2641[二叉树的堂兄弟节点II] 方法一：BFS12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } ...

LCP.P30[魔塔游戏] 方法一：贪心+优先队列123456789101112131415161718192021222324252627class Solution { public int magicTower(int[] nums) { long sum = 0; for (int num : nums) { sum += num; } if (sum < 0) { return -1; } int ans = 0; long hp = 1; PriorityQueue<Integer> q = new PriorityQueue<>(); for (int num : nums) { if (num < 0) { q.offer(num ...

LC.P1686[石子游戏VI] 方法一：贪心+排序123456789101112131415class Solution { public int stoneGameVI(int[] a, int[] b) { int n = a.length; Integer[] index = new Integer[n]; for (int i = 0; i < n; i++) { index[i] = i; } Arrays.sort(index, (i, j) -> a[j] + b[j] - a[i] - b[i]); int diff = 0; for (int i = 0; i < n; i++) { diff += i % 2 == 0 ? a[index[i]] : -b[index[i]]; } return Integer.c ...

CompletableFuture异步多任务最佳实践简介在项目中需要执行异步任务时，通常可以考虑到可以用线程池Executor创建。 如果不需要有返回值，任务实现Runnable接口 如果需要有返回值，任务实现Callable接口，调用Executor的submit方法，再使用Future获取即可 如果多个线程存在依赖组合，可使用同步组件CountDownLatch、CyclicBarrier以及使用起来较为简单的CompeletableFuture等 在Java 8中引入了CompletableFuture，其对Java 5中的Future类提供了非常强大的拓展，可以帮助我们简化异步编程的步骤，并且提供了函数式编程的能力，可以通过回调的方式处理计算结果，也提供了转换和组合CompletableFuture的方法，适用于处理并发的IO密集型任务。 CompletableFuture类图 回顾Future因为CompletableFuture实现了Future接口，因此先回顾Future的用法。 Future是Java 5新加的一个接口，它提供了一种异步并行计算的功能。如果主线程 ...

LC.P2670[找出不同元素数目差数组] 方法一：暴力123456789101112131415161718192021222324class Solution { public int[] distinctDifferenceArray(int[] nums) { Set<Integer> set = new HashSet<>(); int n = nums.length; int[] ans = new int[n]; for (int i = 0; i < n; ++i) { for (int j = 0; j <= i; ++j) { if (!set.contains(nums[j])) { set.add(nums[j]); ans[i]++; } ...

LC.P2859[计算K置位下标对应元素的和] 方法一：模拟(调包)1234567891011121314151617181920class Solution { public int sumIndicesWithKSetBits(List<Integer> nums, int k) { int ans = 0; for (int i = 0; i < nums.size(); ++i) { if (bicCount(i) == k) { ans += nums.get(i); } } return ans; } private int bicCount(int x) { int cnt = 0; while (x > 0) { x &= x - 1; ...