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.

思路：

递归

 1     int min(int a, int b){
 2         if(a < b)
 3             return a;
 4         return b;
 5     }
 6     int minDepth(TreeNode *root) {
 7         // Note: The Solution object is instantiated only once and is reused by each test case.
 8         if(root == NULL)
 9             return 0;
10         if(root->left == NULL && root->right == NULL)
11             return 1;
12         if(root->left == NULL)
13             return 1+minDepth(root->right);
14         if(root->right == NULL)
15             return 1+minDepth(root->left);
16         return 1+min(minDepth(root->left), minDepth(root->right));
17     }