111 Minimum Depth of Binary Tree 二叉树的最小深度

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<TreeNode> que=new LinkedList<TreeNode>();
        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;
    }
}