LeetCode 104. Maximum Depth of Binary Tree

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.

Note: A leaf is a node with no children.

Example:

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

    3
   / \
  9  20
    /  \
   15   7

return its depth = 3.

解析：计算二叉树的最大深度。

采用递归的思路，代码如下：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root) {
        int len = 0;
        if(root == NULL)
            return len;
        int left_len = 0;
        int right_len = 0;
        if(root->left)
            left_len = maxDepth(root->left);
        if(root->right)
            right_len = maxDepth(root->right);
        len += max(left_len, right_len)+1;
        return len;
    }
};