leetcode-MaxDepth of a binaryTree

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.

兩種遞歸：

    int maxDepth(TreeNode* root) {
       if(root==NULL)
        return 0;
        int leftmax=maxDepth(root->left)+1;
        int rightmax=maxDepth(root->right)+1;
        return leftmax>=rightmax?leftmax:rightmax; 
    }
    i
    nt maxDepth(TreeNode* root) {
         if(root==NULL)
        return 0;
        int leftmax=0,rightmax=0;

        if(!root->left&&!root->right) //leaf node
        return 1;

        if(root->left&&root->right)  { // two sons
            leftmax=maxDepth(root->left);
            rightmax=maxDepth(root->right);
            return leftmax>rightmax?(leftmax+1):(rightmax+1);
        }
        if(root->left){//only left son
            return maxDepth(root->left)+1;
        }
        if(root->right){//only right son
            return maxDepth(root->right)+1;
        }

        return 0;// control reaches end of non-void function [-Werror=return-type] 
    }