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.

　　

/**
 * 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;
        int leftNum = 1 + maxDepth(root->left) ;
        int rightNum = 1 + maxDepth(root->right);
        
        int result = leftNum > rightNum ? leftNum: rightNum ;
        
        return result ;
    }
};

 重写：

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void DFS(TreeNode * root, int len){
            
        if(root->left== NULL && root->right == NULL ){
            res = res < len ? len : res;
            return;
        }
        if(root->left != NULL)
            DFS(root->left, len +1);
        if(root->right != NULL)
            DFS(root->right, len+1);
    }
    int  maxDepth(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root == NULL ) return 0;
        res = 0;
        DFS(root, 1);
        return res;
    }
private:
    int res;
};