数据结构与算法之二叉树: LeetCode 513. 找树左下角的值 (Ts版)

找树左下角的值

• https://leetcode.cn/problems/find-bottom-left-tree-value/description/

描述

• 给定一个二叉树的 根节点 root，请找出该二叉树的 最底层 最左边 节点的值
• 假设二叉树中至少有一个节点

示例 1

输入: root = [2,1,3]
输出: 1

示例 2

输入: [1,2,3,4,null,5,6,null,null,7]
输出: 7

提示

• 二叉树的节点个数的范围是 [1,$10^4$]
• -$2^{31}$ <= 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 findBottomLeftValue(root: TreeNode | null): number {
    let curVal = 0;
    const dfs = (root, height) => {
        if (!root) return;
        height++;
        dfs(root.left, height);
        dfs(root.right, height);
        if (height > curHeight) {
            curHeight = height;
            curVal = root.val;
        }
    }

    let curHeight = 0;
    dfs(root, 0);
    return curVal;
};

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 findBottomLeftValue(root: TreeNode | null): number {
    let ret = 0;
    const queue = [root];
    while (queue.length) {
        const p = queue.shift();
        if (p.right) queue.push(p.right);
        if (p.left) queue.push(p.left);
        ret = p.val;
    }
    return ret;
};