【B - The Suspects】

Ideas:

• Disjoint-set basic questions.
• First, write a BFS, MLE .
• Disjoint-set: to make the first element, led by Yuan, each group will merge, and finally look relatively simple.

Code:

• BFS: MLE

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>

using namespace std;

const int maxn = 30005;

int N,M;
int par[maxn];
int ser[maxn];
bool mp[maxn][maxn];
bool sus[maxn];//suspect
int ans;
struct NODE{
	int id;
	int deep;
	NODE(int _id , int _deep) : id(_id) , deep(_deep) {} ;
	friend bool operator > (NODE a,NODE b){
		return a.deep > b.deep ;
	}
};
priority_queue<NODE , vector<NODE> , greater<NODE> > Q;

void INIT(){
	memset(par , -1 , sizeof(par));
	memset(mp , 0 , sizeof(mp));
	memset(sus , 0 ,sizeof(sus));
	ans = 0;
	return ;
}

void BFS(){
	Q.push(NODE(0 , 0)) ;
	sus[0] = true;
	while(Q.size()){
		NODE cur = Q.top() ; Q.pop() ;
		int id = cur.id ;
		int deep = cur.deep ;
		for(int i=0;i<N;i++){
			if(id != i && mp[i][id] && !sus[i]){
				sus[i] = true;
				Q.push(NODE(i , deep+1));
			}
		}
	}
	for(int i=0;i<N;i++)
		if(sus[i])
			ans++;
	return ; 
}

int main(){
	while(scanf("%d%d" , &N , &M) && (N || M)){
		INIT();
		while(M--){
			int k;
			scanf("%d" , &k) ;
			for(int i=1;i<=k;i++)
				scanf("%d" , ser + i);
			for(int i=1;i<=k;i++)
				for(int j=1;j<=k;j++)
					mp[ser[i]][ser[j]] = mp[ser[j]][ser[i]] = true;
		}
		BFS();
		printf("%d\n" , ans);
	}
	return 0;
}​

• Disjoint-set: 16ms 800kB

​//16ms		800kB


#include <iostream>
#include <cstring>
#include <cstdio>

using namespace std;

const int maxn = 30005;

int M,N;
int ans;
int par[maxn];

void INIT(){
	ans = 0;
	memset(par , -1 , sizeof(par));
	return ;
}

int FIND(int i){
	return par[i] == -1 ? i : par[i] = FIND(par[i]);
}

void UNION(int u,int v){
	int paru = FIND(u);
	int parv = FIND(v);
	if(paru != parv)
		par[paru] = parv;
		//注意不是：par[u] = v; 
	return ;
}

int main(){
	while(~scanf("%d%d" , &N , &M) && (M||N)){
		INIT();
		while(M--){
			int k;
			int temp;
			scanf("%d%d" , &k , &temp);
			k--;
			while(k--){
				int id;
				scanf("%d" , &id);
				UNION(id , temp);
			}
		}
		for(int i=0;i<N;i++)
			if(FIND(0) == FIND(i))
				ans++;
		printf("%d\n" , ans) ;
	}
	return 0;
}​