题解

#include<bits/stdc++.h>
using namespace std;
int a[101][101],c , maxs = 0;
bool visit[101][101] = {0};
int n, m;
int dx[4] = {-1,0,1,0};
int dy[4] = {0,-1,0,1};

void search(int x,int y){
	visit[x][y] = 1;
	c++;
	for (int i = 0; i <= 3; i++){
		int xx = x + dx[i];
		int yy = y + dy[i];
		if (visit[xx][yy] == 0 && a[xx][yy] == 1 && xx > 0 && yy > 0 && xx <= n && yy <= m){
			search(xx,yy);
		}
	}
	
}

int main(){
	cin >> n;
	cin >> m;
	for (int i = 1; i <= n; i++){
		for (int j = 1; j <= m; j++){
			cin >> a[i][j];
		}
	}
	for (int i = 1; i <= n; i++){
		for (int j = 1; j <= m; j++){
			if (visit[i][j] == 0 && a[i][j]){
				c = 0;
				search(i,j);
			}
			maxs = max(c, maxs);
		}
	}
	cout << maxs;
}