/** * 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;        Queue
     
       q=new LinkedList
      
       ();        q.offer(root);        int size=q.size();        int res=1;        int count=0;        while(!q.isEmpty())        {            TreeNode temp=q.poll();            if(temp.left==null&&temp.right==null)            {                //找到了叶子节点                break;            }            if(temp.left!=null)                q.offer(temp.left);            if(temp.right!=null)                q.offer(temp.right);            count++;            if(count==size)            {                count=0;                size=q.size();                res++;            }                                }        return res;    }}