Javascript(leetcode#104) Maximum Depth of Binary Tree

Difficult:Easy

題目

Given the root of a binary tree, return its maximum depth.

A binary tree’s maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

翻譯

給定二叉樹的根，返回其最大深度。

二叉樹的最大深度是從根節點到最遠葉節點的最長路徑上的節點數。

範例

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: 3

Example 2:

Input: root = [1,null,2]
Output: 2

解題思路

1.利用遞迴搜尋
2.找出最大的深度

Solution

var maxDepth = function (root) {
    let depth=0;
    let trace = function (root, num) {
        if (root == null) return;
        trace(root.left, num + 1);
        trace(root.right, num + 1);
        depth=Math.max(num,depth);
    }
    trace(root, 1);
    return depth;
};