111. 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.
題意：找出二叉樹的最小深度。

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