leetcode104. maximum depth of binary tree

 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class  {
public:
    int maxDepth(TreeNode* root) {
        if(root==NULL)			//递归出口，到达叶子结点
            return 0;		
        int maxLeft=maxDepth(root->left);		//左右子树
        int maxRight=maxDepth(root->right);
        return (maxLeft>maxRight)?maxLeft+1:maxRight+1;
    }
};