18491 岛屿的数量

18491 岛屿的数量

⭐️难度：中等

🌟考点：搜索

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import java.util.*;

public class Main {
    static int[][] a = new int[505][505];
    static int[] dx = {0,0,1,-1};
    static int n;
    static int[] dy = {1,-1,0,0};  // 用数组表示移动方向，分别对应 右 左 上 下

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        n = sc.nextInt();
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= n; j++) {
                a[i][j] = sc.nextInt();
            }
        }

        int ans = 0;
        for (int i = 1; i <= n; i++) {
            for (int j = 0; j <= n; j++) {
                if(a[i][j] == 1){
                    bfs(i,j);
                    ans ++;
                }
            }
        }
        System.out.println(ans);
    }

    static void bfs(int x,int y){
        a[x][y] = 0; // 访问过的陆地变成海洋
        for (int i = 0; i < 4; i++) {
            for (int j = 0; j < 4; j++) {
                int ax = dx[i] + x;
                int ay = dy[i] + y;
                if(ax < 1 || ay < 1 || ax > n + 1 || ay > n + 1 || a[ax][ay] == 0) continue; // 检查坐标合法，且是陆地
                bfs(ax,ay);
            }
        }
    }
}

🍎笔记