Maximum Depth of Binary Tree 树的最大深度

/**
 * 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) {
        if(root==NULL)
            return 0;
        int i=maxDepth(root->left)+1;
        int j=maxDepth(root->right)+1;
        return max(i,j);
    }
};