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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, 1 0 4 10^4 104]
- − 2 31 -2^{31} −231 <= Node.val <= 2 31 2^{31} 231 - 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;
};