给定一个二叉树，找出其最小深度。

最小深度是从根节点到最近叶节点的最短路径的节点数量。

详见：https://leetcode.com/problems/minimum-depth-of-binary-tree/description/

Java实现：

递归实现：

/** * 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 minLeft=minDepth(root.left);        int minRight=minDepth(root.right);        if(minLeft==0||minRight==0){            return minLeft>=minRight?minLeft+1:minRight+1;        }        return Math.min(minLeft,minRight)+1;    }}

非递归实现：

/** * 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;        }        LinkedList
     
       que=new LinkedList
      
       ();        que.offer(root);        int node=1;        int level=1;        while(!que.isEmpty()){            root=que.poll();            --node;            if(root.left==null&&root.right==null){                return level;            }            if(root.left!=null){                que.offer(root.left);            }            if(root.right!=null){                que.offer(root.right);            }            if(node==0){                node=que.size();                ++level;            }        }        return level;    }}