主体

import java.util.*;
class Main{

    public static void main(String[] args){
        Scanner scan=new Scanner(System.in);
        int r=scan.nextInt(),c=scan.nextInt();
        int[][] grid=new int[r][c];
        for(int i=0;i<r;i++){
            for(int j=0;j<c;j++){
                grid[i][j]=scan.nextInt();
            }
        }
        System.out.println(helper(grid));
    }


    static int helper(int[][] grid){
        int rows=grid.length,cols=grid[0].length;
        int ans=0;
        for(int r=0;r<rows;r++){
            for(int c=0;c<cols;c++){
                if(grid[r][c]==1){
                    ans++;
                    //抹去arr里的1
                    //dfs(grid,r,c);
                    bfs(grid,r,c);
                }
            }
        }
        return ans;
    }
}

深度优先
在进入dfs前尽量剪枝，不要等进来了再剪枝，可能会栈溢出

static void dfs(int[][] grid,int r,int c){
    if(r>=0 && r<grid.length && c>=0 && c<grid[0].length && grid[r][c]==1){
        grid[r][c]=0;
        for(int i=-1;i<=1;i++){
            for(int j=-1;j<=1;j++){
                int x=r+i,y=c+j;
                dfs(grid,x,y);
            }
        }
    }
}

广度优先

static class Point {
    int r;
    int c;

    Point(int i, int j) {
        r = i;
        c = j;
    }
}

private static void bfs(int[][] grid, int r, int c) {
    Queue<Point> q=new LinkedList();
    q.offer(new Point(r,c));
    grid[r][c]=0;
    while(!q.isEmpty()){
        Point temp=q.poll();
        for(int i=-1;i<=1;i++){
            for(int j=-1;j<=1;j++){
                int x=temp.r+i,y=temp.c+j;
                if(x>=0 && x<grid.length && y>=0 && y<grid[0].length && grid[x][y]==1){
                    q.offer(new Point(x,y));
                    grid[x][y]=0;
                }
            }
        }
    }
}