[LeetCode] 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.

这道题非常直接，只需要递归深搜就可以。需要注意的是递归的终止条件：root为空，深度为0；root没有孩子，深度为1。如果存在孩子，则递归深搜下去。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode *root) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(root == NULL)
            return 0;
        
        if(root -> left == NULL && root -> right == NULL)
            return 1;
        
        int leftDepth = 0, rightDepth = 0;
        if(root -> left != NULL)
            leftDepth = maxDepth(root -> left) + 1;
        if(root -> right != NULL)
            rightDepth = maxDepth(root -> right) + 1;
        
        return (leftDepth > rightDepth) ? leftDepth : rightDepth;
        
    }
    
};

写完后看了博客园另一位博主的写法，发现自己的第一个if其实只是为了填补后面写的代码的漏洞，这个问题完全可以用精简得多的方式写出来。/ * Definition for binary tree

 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (root == NULL)
            return 0;
        
        return max(maxDepth(root->left),maxDepth(root->right)) + 1;
    }
};