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在每个树行中找最大值

• https://leetcode.cn/problems/find-largest-value-in-each-tree-row/description/

描述

• 给定一棵二叉树的根节点 root ，请找出该二叉树中每一层的最大值

示例1

输入: root = [1,3,2,5,3,null,9]
输出: [1,3,9]

示例2

输入: root = [1,2,3]
输出: [1,3]

提示

• 二叉树的节点个数的范围是 [0,$10^4$]
• $-2^{31}$ <= Node.val <= $2^{31}$ - 1

Typescript 版算法实现

1 ) 方案1：深度优先搜索

/*** Definition for a binary tree node.* class TreeNode {*     val: number*     left: TreeNode | null*     right: TreeNode | null*     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {*         this.val = (val===undefined ? 0 : val)*         this.left = (left===undefined ? null : left)*         this.right = (right===undefined ? null : right)*     }* }*/function largestValues(root: TreeNode | null): number[] {if (!root) return [];const res = [];const dfs = (res, root, curHeight) => {if (curHeight === res.length) {res.push(root.val);} else {res.splice(curHeight, 1, Math.max(res[curHeight], root.val));}if (root.left) {dfs(res, root.left, curHeight + 1);}if (root.right) {dfs(res, root.right, curHeight + 1);}}dfs(res, root, 0);return res;
};

2 ) 方案2：广度优先搜索

/*** Definition for a binary tree node.* class TreeNode {*     val: number*     left: TreeNode | null*     right: TreeNode | null*     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {*         this.val = (val===undefined ? 0 : val)*         this.left = (left===undefined ? null : left)*         this.right = (right===undefined ? null : right)*     }* }*/function largestValues(root: TreeNode | null): number[] {if (!root) return [];const res = [];const queue = [root];while (queue.length) {let len = queue.length;let maxVal = -Number.MAX_VALUE;while (len > 0) {len--;const t = queue.shift();maxVal = Math.max(maxVal, t.val);if (t.left) {queue.push(t.left);}if (t.right) {queue.push(t.right);}}res.push(maxVal);}return res;
};