題目：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.

?

/**

?* Definition for binary tree

?* public class TreeNode {

?*???? int val;

?*???? TreeNode left;

?*???? TreeNode right;

?*???? TreeNode(int x) { val = x; }

?* }

?*/

import java.util.*;

public class Solution {

??? public int run(TreeNode root) {

??????? if(root==null)

??????????? return 0;

??????? if(root.left==null&&root.right==null)

??????????? return 1;

?

//方法一：遞歸

???? /*?? if(root.left==null)// 若左子樹為空，則返回右子樹的最小深度+1

??????????? return run(root.right)+1;

??????? if(root.right==null)

??????????? return run(root.left)+1;

???????

??????? int l=run(root.left);

??????? int r=run(root.right);

???????

??????? return (l>r)?(r+1):(l+1);

??????? */

? ? ? ?//方法二

??????? Queue<TreeNode> q=new LinkedList<>();

?????? // 思路是層序遍歷，找到第一個(gè)左右結(jié)點(diǎn)都為null的情況，就返回

??????? q.add(root);

??????? int level=0;

??????? while(!q.isEmpty()){

??????????? int size=q.size();

???????????? level++;

??????????? for(int i=0;i<size;i++){

??????????????? TreeNode node=q.poll();

??????????????? if(node.left==null&&node.right==null)

??????????????????? return level;

??????????????? if(node.left!=null)

??????????????????? q.add(node.left);

??????????????? if(node.right!=null)

??????????????? ????q.add(node.right);

???????????????

??????????? }

??????????

??????? }

???????

??????? return level;

??? }

}

轉(zhuǎn)載于:https://www.cnblogs.com/xiaolovewei/p/8029796.html

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