g0901_1000.s0909_snakes_and_ladders.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

There is a newer version: 1.35

package g0901_1000.s0909_snakes_and_ladders;

// #Medium #Array #Breadth_First_Search #Matrix
// #2022_03_28_Time_7_ms_(79.52%)_Space_47.7_MB_(58.43%)

import java.util.LinkedList;
import java.util.Queue;

public class Solution {
    private int size;

    public int snakesAndLadders(int[][] board) {
        Queue queue = new LinkedList<>();
        size = board.length;
        int target = size * size;
        boolean[] visited = new boolean[target];
        queue.add(1);
        visited[0] = true;
        int step = 0;
        while (!queue.isEmpty()) {
            int queueSize = queue.size();
            for (int i = 0; i < queueSize; i++) {
                int previousLabel = queue.poll();
                if (previousLabel == target) {
                    return step;
                }
                for (int currentLabel = previousLabel + 1;
                        currentLabel <= Math.min(target, previousLabel + 6);
                        currentLabel++) {
                    if (visited[currentLabel - 1]) {
                        continue;
                    }
                    visited[currentLabel - 1] = true;
                    int[] position = indexToPosition(currentLabel);
                    if (board[position[0]][position[1]] == -1) {
                        queue.add(currentLabel);
                    } else {
                        queue.add(board[position[0]][position[1]]);
                    }
                }
            }
            step++;
        }

        return -1;
    }

    private int[] indexToPosition(int index) {
        int vertical = this.size - 1 - (index - 1) / this.size;
        int horizontal;
        if ((this.size - vertical) % 2 == 1) {
            horizontal = (index - 1) % this.size;
        } else {
            horizontal = this.size - 1 - (index - 1) % this.size;
        }
        return new int[] {vertical, horizontal};
    }
}