View Code of Problem 1042

#include <iostream>
#include <cstdio>
#include <vector>
#include <cstring>
#include <queue>
# define INF 0x7FFFFFFF
using namespace std;
int n,m;
int minn;
struct node {
    int u,f;
};
int sum[505];
int tmp,ok;
vector<int> v[505];

void init() {
    for(int i=0; i<=n; i++) {
        v[i].clear();
    }
    memset(sum,-1,sizeof(sum));
}

void bfs(int u0) {
    queue<node> q;
    node t;
    t.f = -1;
    t.u = u0;
    sum[u0] = 0;
    q.push(t);
    while(! q.empty()) {
        t = q.front();
        node tt;
        q.pop();
        int size = v[t.u].size();
        for(int i=0; i<size; i++) {
            tt.f = t.u;
            tt.u = v[t.u][i];
            if(tt.u == t.f)
                continue;
            if(sum[tt.u] == -1) {
                q.push(tt);
                sum[tt.u] = sum[t.u] + 1;
            } else if(sum[tt.u] + sum[t.u] > 1 ) {
                int tmp = sum[tt.u] + sum[t.u] + 1;
                if(minn > tmp) minn = tmp;
            }
        }
    }
}

int main() {
    int t,i,j,a,b;
    cin >> t;
    int casee = 1;
    while(t --) {
        scanf("%d%d",&n,&m);
        init();
        for(i=0; i<m; i++) {
            scanf("%d%d",&a,&b);
            v[a].push_back(b);
            v[b].push_back(a);
        }
        printf("Case %d: ",casee++);
        minn = INF;
        for(i=0; i<n; i++) {
            memset(sum,-1,sizeof(sum));
            //ok = 0;
            bfs(i);
        }
        if(minn == INF) cout << "impossible" << endl;
        else cout << minn << endl;
    }
    return 0;
}