天梯赛 L2 红色警报

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/ccDLlyy/article/details/79807676

题目链接：点击打开链接

思路：每失去一个城市，判断连通分量是否增加，若增加，则发出红色警报。

#include <cstdio>
#include <cstring>
#include <iostream>
#include <queue>
using namespace std;
int n,m,map[505][505];
int book[505],flag[505];
void bfs(int x){
	queue<int> q;
	q.push(x);
	book[x] = 1;
	while(!q.empty()){
		int t = q.front();
		q.pop();
		for(int i = 0;i < n;i++){
			if(flag[i] == 0 && map[t][i] == 1 && !book[i]){
				q.push(i);
				book[i] = 1;
			}
		}
	}
}
int main(){
	int x,y,cnt;
	scanf("%d%d",&n,&m);
	memset(map,0,sizeof(map));
	memset(flag,0,sizeof(flag));
	for(int i = 0;i < m;i++){
		scanf("%d%d",&x,&y);
		map[x][y] = map[y][x] = 1;
	}
	cnt = 0;
	memset(book,0,sizeof(book));
	for(int i = 0;i < n;i++){
		if(!book[i]){
			bfs(i);
			cnt++;
		}
	}
	int q,cnt1;
	scanf("%d",&q);
	for(int i = 0;i < q;i++){
		scanf("%d",&x);
		flag[x] = -1;
		cnt1 = 0;
		memset(book,0,sizeof(book));
		for(int i = 0;i < n;i++){
			if(flag[i] == 0 && !book[i]){
				bfs(i);
				cnt1++;
			}
		}
		if(cnt1 > cnt){
			printf("Red Alert: City %d is lost!\n",x);
		}
		else{
			printf("City %d is lost.\n",x);
		}
		cnt = cnt1;
	}
	if(q == n){
		printf("Game Over.\n");
	}
	return 0;
}