HDU4460-Friend Chains-BFS+bitset优化

bfs的时候用bitset优化一下。

水题

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <queue>
#include <unordered_map>

using namespace std;

const int maxn = 1e3+10;
int N,M;
unordered_map<string,int> mp;

bitset<maxn> G[maxn];
bitset <maxn> to,unvis;
queue <int> Q;

int dis[maxn];
int bfs(int rt)
{
    while(!Q.empty()) Q.pop();
    Q.push(rt);
    dis[rt] = 0;

    unvis.reset();
    for(int i=1;i<=N;i++) unvis.set(i);
    int res = 0;
    unvis.reset(rt);

    while(!Q.empty())
    {
        int u = Q.front();
        Q.pop();
        to = unvis & G[u];
        for(int v = to._Find_first(); v<=N; v = to._Find_next(v))
        {
            Q.push(v);
            unvis.reset(v);
            dis[v] = dis[u]+1;
            res = max(res,dis[v]);
        }
    }
    //printf("")
    if(unvis.any()) return -1;
    return res;
}

int main()
{
    while(scanf("%d",&N) && N)
    {
        mp.clear();
        for(int i=0;i<maxn;i++) G[i].reset();
        for(int i=1;i<=N;i++)
        {
            char tmp[50];
            scanf("%s",tmp);
            mp[tmp] = i;
        }
        scanf("%d",&M);
        for(int i=0;i<M;i++)
        {
            char tmp1[50],tmp2[50];
            scanf("%s %s",tmp1,tmp2);
            int u = mp[tmp1],v = mp[tmp2];
            //printf("add edge:%d %d
",u,v);
            G[u].set(v);G[v].set(u);
        }

        int ans = 0;
        bool unconnected = 0;
        for(int i=1;i<=N;i++)
        {
            int res = bfs(i);
            if(res == -1){unconnected = true;break;}
            ans = max(ans,res);
        }
        if(unconnected) printf("-1
");
        else printf("%d
",ans);
    }
}