353 Design Snake Game
Problem:
Design a Snake game that is played on a device with screen size = width x height. Play the game online if you are not familiar with the game.
The snake is initially positioned at the top left corner (0,0) with length = 1 unit.
You are given a list of food's positions in row-column order. When a snake eats the food, its length and the game's score both increase by 1.
Each food appears one by one on the screen. For example, the second food will not appear until the first food was eaten by the snake.
When a food does appear on the screen, it is guaranteed that it will not appear on a block occupied by the snake.
Example:
Given width = 3, height = 2, and food = [[1,2],[0,1]].
Snake snake = new Snake(width, height, food);
Initially the snake appears at position (0,0) and the food at (1,2).
|S| | |
| | |F|
snake.move("R"); -> Returns 0
| |S| |
| | |F|
snake.move("D"); -> Returns 0
| | | |
| |S|F|
snake.move("R"); -> Returns 1 (Snake eats the first food and right after that, the second food appears at (0,1) )
| |F| |
| |S|S|
snake.move("U"); -> Returns 1
| |F|S|
| | |S|
snake.move("L"); -> Returns 2 (Snake eats the second food)
| |S|S|
| | |S|
snake.move("U"); -> Returns -1 (Game over because snake collides with border)
Solutions:
public class SnakeGame {
private List<Integer> xs;
private List<Integer> ys;
private HashSet<String> snake;
private int foodx;
private int foody;
private int[][] food;
private int eaten;
private int m;
private int n;
public SnakeGame(int width, int height, int[][] food) {
xs = new LinkedList<Integer>();
ys = new LinkedList<Integer>();
snake = new HashSet<String>();
this.food = food;
eaten = 0;
m = height;
n = width;
xs.add(0, 0);
ys.add(0, 0);
snake.add(0 + "," + 0);
if (food != null && food.length > 0) {
foodx = food[0][0];
foody = food[0][1];
}
else {
foodx = -1;
foody = -1;
}
}
private boolean die(int i, int j) {
if (i < 0 || i >= m || j < 0 || j >= n) {
return true;
}
return snake.contains(i + "," + j) && !(i == xs.get(xs.size() - 1) && j == ys.get(ys.size() - 1));
}
public int move(String direction) {
int hx = xs.get(0), hy = ys.get(0);
if (direction.equals("U")) {
hx --;
}
else if (direction.equals("L")) {
hy --;
}
else if (direction.equals("R")) {
hy ++;
}
else if (direction.equals("D")) {
hx ++;
}
else {
System.out.println("wrong move");
}
if (die(hx, hy)) {
return -1;
}
if (!(hx == foodx && hy == foody)) {
xs.add(0, hx);
ys.add(0, hy);
snake.remove(xs.get(xs.size() - 1) + "," + ys.get(ys.size() - 1));
snake.add(hx + "," + hy);
xs.remove(xs.size() - 1);
ys.remove(ys.size() - 1);
return eaten;
}
eaten ++;
xs.add(0, hx);
ys.add(0, hy);
snake.add(hx + "," + hy);
if (food != null && eaten < food.length) {
foodx = food[eaten][0];
foody = food[eaten][1];
}
else {
foodx = -1;
foody = -1;
}
return eaten;
}
}
public class SnakeGame {
int[][] food;
int m, n;
int headX, headY;
int eaten;
private HashSet<String> snake;
LinkedList<int[]> queue;
public SnakeGame(int width, int height, int[][] food) {
this.food=food;
snake = new HashSet<String>();
eaten = 0;
headX =0;
headY =0;
m = height;
n = width;
queue= new LinkedList<int[]>();
queue.offer(new int[]{0, 0});
snake.add("0,0");
}
public int move(String direction) {
if (direction.equals("U")) {
headX --;
}
else if (direction.equals("L")) {
headY --;
}
else if (direction.equals("R")) {
headY ++;
}
else if (direction.equals("D")) {
headX ++;
}
else {
System.out.println("Wrong move");
}
if(!isValid(headX,headY)){
return -1;
}
return process(headX, headY);
}
public boolean isValid(int i, int j){
if(i < 0 || i >= m || j < 0 || j >= n)
return false;
return true;
}
public int process(int x, int y){
if(eaten == food.length){
snake.remove(queue.peek()[0] + "," + queue.peek()[1]);
queue.poll();
}else if(food[eaten][0]==x && food[eaten][1]==y){
eaten ++;
}else{
snake.remove(queue.peek()[0] + "," + queue.peek()[1]);
queue.poll();
}
if (snake.contains(x + "," + y)) {
return -1;
}
snake.add(x + "," + y);
queue.offer(new int[]{x,y});
return eaten;
}
}