hdu5876 Sparse Graph（补图最短路 bfs）

题目链接：hdu5876 Sparse Graph

详见代码。。

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#include<vector>
#include<set>
using namespace std;
const int N = 200001;
const int inf = 0x3f3f3f3f;
int n, m;
vector<vector<int> >g;
int d[N];
void bfs(int s){
    int u,v,i,j;
    queue<int>q;
    set<int>a; //不邻接的点
    set<int>b; //未扩展的点
    set<int>::iterator it;
    for(i = 1; i <= n; ++i)
        a.insert(i);
    a.erase(s);
    q.push(s);
    while(!q.empty()){
        u=q.front();
        q.pop();
        for(j=0;j<g[u].size();++j){
            v=g[u][j];
            if(!a.count(v))
                continue;
            b.insert(v);
            a.erase(v);
        }
        for(it = a.begin(); it != a.end(); it++){
            d[*it] = d[u] + 1;
            q.push(*it);
        }
        a.swap(b);
        b.clear();
    }
}
int main(){
    int t, i, j, x, y, s, f;
    scanf("%d", &t);
    while(t--){
        scanf("%d %d", &n, &m);
        memset(d, inf, sizeof(d));
        g.clear();
        g.resize(N+1);
        for(i = 0; i < m; ++i){
            scanf("%d %d", &x, &y);
            g[x].push_back(y);
            g[y].push_back(x);
        }
        scanf("%d", &s);
        d[s] = 0;
        bfs(s);
        f = 0;
        for(i = 1; i <= n; ++i){
            if(i == s)continue;
            if(d[i] == inf)
                printf("-1
");
            else if(!f){
                printf("%d", d[i]);
                f = 1;
            }
            else
                printf(" %d",d[i]);
        }
        printf("
");
    }
    return 0;
}