Leetcode: The Maze II
There is a ball in a maze with empty spaces and walls. The ball can go through empty spaces by rolling up, down, left or right, but it won't stop rolling until hitting a wall. When the ball stops, it could choose the next direction. Given the ball's start position, the destination and the maze, find the shortest distance for the ball to stop at the destination. The distance is defined by the number of empty spaces traveled by the ball from the start position (excluded) to the destination (included). If the ball cannot stop at the destination, return -1. The maze is represented by a binary 2D array. 1 means the wall and 0 means the empty space. You may assume that the borders of the maze are all walls. The start and destination coordinates are represented by row and column indexes. Example 1 Input 1: a maze represented by a 2D array 0 0 1 0 0
0 0 0 0 0
0 0 0 1 0
1 1 0 1 1
0 0 0 0 0 Input 2: start coordinate (rowStart, colStart) = (0, 4)
Input 3: destination coordinate (rowDest, colDest) = (4, 4) Output: 12
Explanation: One shortest way is : left -> down -> left -> down -> right -> down -> right.
The total distance is 1 + 1 + 3 + 1 + 2 + 2 + 2 = 12.
Example 2 Input 1: a maze represented by a 2D array 0 0 1 0 0
0 0 0 0 0
0 0 0 1 0
1 1 0 1 1
0 0 0 0 0 Input 2: start coordinate (rowStart, colStart) = (0, 4)
Input 3: destination coordinate (rowDest, colDest) = (3, 2) Output: -1
Explanation: There is no way for the ball to stop at the destination.
Note:
There is only one ball and one destination in the maze.
Both the ball and the destination exist on an empty space, and they will not be at the same position initially.
The given maze does not contain border (like the red rectangle in the example pictures), but you could assume the border of the maze are all walls.
The maze contains at least 2 empty spaces, and both the width and height of the maze won't exceed 100.
Solution of The Maze: https://discuss.leetcode.com/topic/77471/easy-understanding-java-bfs-solution
Solution of The Maze III: https://discuss.leetcode.com/topic/77474/similar-to-the-maze-ii-easy-understanding-java-bfs-solution
We need to use PriorityQueue
instead of standard queue, and record the minimal length of each point.
public class Solution {
class Point {
int x,y,l;
public Point(int _x, int _y, int _l) {x=_x;y=_y;l=_l;}
}
public int shortestDistance(int[][] maze, int[] start, int[] destination) {
int m=maze.length, n=maze[0].length;
int[][] length=new int[m][n]; // record length
for (int i=0;i<m*n;i++) length[i/n][i%n]=Integer.MAX_VALUE;
int[][] dir=new int[][] {{-1,0},{0,1},{1,0},{0,-1}};
PriorityQueue<Point> list=new PriorityQueue<>((o1,o2)->o1.l-o2.l); // using priority queue
list.offer(new Point(start[0], start[1], 0));
while (!list.isEmpty()) {
Point p=list.poll();
if (length[p.x][p.y]<=p.l) continue; // if we have already found a route shorter
length[p.x][p.y]=p.l;
for (int i=0;i<4;i++) {
int xx=p.x, yy=p.y, l=p.l;
while (xx>=0 && xx<m && yy>=0 && yy<n && maze[xx][yy]==0) {
xx+=dir[i][0];
yy+=dir[i][1];
l++;
}
xx-=dir[i][0];
yy-=dir[i][1];
l--;
list.offer(new Point(xx, yy, l));
}
}
return length[destination[0]][destination[1]]==Integer.MAX_VALUE?-1:length[destination[0]][destination[1]];
}
}
Leetcode: The Maze II的更多相关文章
- [LeetCode] The Maze II 迷宫之二
There is a ball in a maze with empty spaces and walls. The ball can go through empty spaces by rolli ...
- [LeetCode] The Maze III 迷宫之三
There is a ball in a maze with empty spaces and walls. The ball can go through empty spaces by rolli ...
- [LeetCode] The Maze 迷宫
There is a ball in a maze with empty spaces and walls. The ball can go through empty spaces by rolli ...
- [LeetCode] Palindrome Partitioning II 解题笔记
Given a string s, partition s such that every substring of the partition is a palindrome. Return the ...
- [leetcode]Word Ladder II @ Python
[leetcode]Word Ladder II @ Python 原题地址:http://oj.leetcode.com/problems/word-ladder-ii/ 参考文献:http://b ...
- LeetCode:课程表II【210】
LeetCode:课程表II[210] 题目描述 现在你总共有 n 门课需要选,记为 0 到 n-1. 在选修某些课程之前需要一些先修课程. 例如,想要学习课程 0 ,你需要先完成课程 1 ,我们用一 ...
- LeetCode:全排列II【47】
LeetCode:全排列II[47] 参考自天码营题解:https://www.tianmaying.com/tutorial/LC47 题目描述 给定一个可包含重复数字的序列,返回所有不重复的全排列 ...
- A Dangerous Maze (II) LightOJ - 1395(概率dp)
A Dangerous Maze (II) LightOJ - 1395(概率dp) 这题是Light Oj 1027的加强版,1027那道是无记忆的. 题意: 有n扇门,每次你可以选择其中一扇.xi ...
- LeetCode:子集 II【90】
LeetCode:子集 II[90] 题目描述 给定一个可能包含重复元素的整数数组 nums,返回该数组所有可能的子集(幂集). 说明:解集不能包含重复的子集. 示例: 输入: [1,2,2] 输出: ...
随机推荐
- SQL反模式学习笔记8 多列属性
目标:存储多值属性 反模式:创建多个列.比如一个人具有多个电话号码.座机号码.手机号码等. 1.查询:多个列的话,查询时可能不得不用IN,或者多个OR: 2.添加.删除时确保唯一性.判断是否有值:这些 ...
- Innodb与Myisam引擎的区别与应用场景
1. 区别: (1)事务处理: MyISAM是非事务安全型的,而InnoDB是事务安全型的(支持事务处理等高级处理): (2)锁机制不同: MyISAM是表级锁,而InnoDB是行级锁: (3)sel ...
- Java菜鸟浅谈OCR
什么是OCR? 粗暴点说就是图片文本识别!正规点的说法就是:(Optical Character Recognition,光学电子识别) 最近公司开展新项目,考虑到实名认证这方面,然后还要上传身份证正 ...
- Yii2 验证规则
验证器的使用方法: public function rules() { return [ [['email', 'password'], 'required'], ['password', 'stri ...
- weblogic10.3 启动报错 Unrecognized option: -jrockit Error: Could not create the Java Virtual Machine
今天在使用weblogic10.3+jdk7创建domain的时候,建好domain后启动报如下错误信息: Unrecognized option: -jrockitError: Could not ...
- 如何彻底卸载Jenkins
起因: 最近在做持续集成测试过程中遇到一个问题,之前部署的Jenkins管理员密码忘了之后无法登陆,而且删除掉tomcat下webapps文件夹中的Jenkins目录后,再次安装Jenkins后相关的 ...
- 使用MDI 和 XtraTabbedMdiManager 后 选项卡切换后Ribbon 合并后不选中MDI子窗...
使用MDI 和 XtraTabbedMdiManager 后 选项卡切换后Ribbon 合并后不选中MDI子我这里是 继承 XtraTabbedMdiManager 所以,是重载的 OnSelec ...
- c++库函数 Map
转载:https://blog.csdn.net/shuzfan/article/details/53115922 C++中map提供的是一种键值对容器,里面的数据都是成对出现的,如下图:每一对中的第 ...
- linux权限字母的含义
无 --- 只能列出文件 r-- 访问文件 r-x 创建和删除文件 rwx
- python3 Django集成Ueditor富文本编辑器
1.下载 python3: https://github.com/twz915/DjangoUeditor3/ (直接下载zip) 2.解压,解压打开后找到DjangoUeditor将DjangoUe ...