LeetCode | 104. Maximum Depth of Binary Tree

题目：

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

For example:
Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its depth = 3.

题意：

求出输入二叉树的最深高度，并返回输出。我的想法是使用回溯将二叉树遍历一遍，并记录最深的高度值max，并进行更新。

代码：

void backtrack(TreeNode* root, int cur, int& max) {
        if(root->left == NULL && root->right == NULL && max < cur+1)
        {
            max = cur+1;
            return;
        }
        if(root->left != NULL)
        {
            backtrack(root->left, cur+1, max);
        }
        if(root->right != NULL)
        {
            backtrack(root->right, cur+1, max);
        }
        return;
    }
    int maxDepth(TreeNode* root) {
        if(root == NULL)
            return 0;
        int max = 0, cur = 0;
        backtrack(root, cur, max);
        return max;
    }

一次AC^____________________^四月快乐！