LeetCode:Minimum Depth of Binary Tree

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

class Solution{
public:
    int minDepth(TreeNode *root){
        if(root==NULL)
        {
            return 0;
        }
        if(root->left==NULL&&root->right==NULL)
        {
            return 1;
        }
        else
        {
            int a=minDepth(root->left);
            int b=minDepth(root->right);
            if(a==0||b==0)
            {
                return (a>b?a:b)+1;
            }
            else
            {
                return (a<b?a:b)+1;
            }
        }
    }
};