LeetCode之求二叉树最小深度

1. 题目描述

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.

题意：给出一个二叉树，求该二叉树的最小深度（从叶节点到根结点的最小值）。

2. 解题思路

按照广度遍历的顺序，找到第一个叶子节点，该节点到根结点的距离即为该二叉树最小深度。

3. 代码实现

package com.tree.deepth;

import java.util.*;

/**
 * @author zhulongkun20@163.com
 * @since 2018/11/2 下午7:43
 */
public class Solution {
    public int run1(TreeNode root) {
        if (root == null)
            return 0;
        LinkedList<TreeNode> queue = new LinkedList<>();
        int level = 1;
        TreeNode last, now;
        last = now = root;
        queue.add(root);
        while (queue.size() != 0) {
            TreeNode node = queue.poll();
            if (node.left != null)
                queue.add(node.left);
            if (node.right != null)
                queue.add(node.right);
            if (node.left == null && node.right == null)
                return level;
            if (node == last) {
                level++;
                last = queue.getLast();
            }
        }
        return level;
    }
}