leetcode-Minimum Depth of Binary Tree

/**
 * 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 minDepth(TreeNode *root) {
        if(root==NULL)
            return 0;
        
        int l=minDepth(root->left);
        int r=minDepth(root->right);
        
        if(l==0&&r==0)
            return 1;
        if(l==0||r==0)
            return l>r?l+1:r+1;
        if(l!=0&&r!=0)
            return l>r?r+1:l+1;
    }
};