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：求一棵树的最小深度可以转化为求左子树和右子树的最小深度，然后加上1即可，注意判断递归的出口。

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int minDepth(TreeNode root) {
if(root==null) return 0;
if(root.left==null && root.right==null) return 1;
if(root.left==null) return minDepth(root.right)+1;
if(root.right==null) return minDepth(root.left)+1;
int left=minDepth(root.left);
int right=minDepth(root.right);
return Math.min(left,right)+1;

}

}