HDU 6005 Pandaland

来源：互联网发布：一键越狱软件编辑：程序博客网时间：2024/06/06 03:29

题意：给一个带权无向图，求图中能成环的权值最小值，如果不能成环，输出-1；
分析：
暴力+dijkstra。枚举每一条边，然后用dijkstra求s到t的距离（其中舍去s-t这条边）。
dijkstra找到t就跳出，或出队列的距离 >= 当前找到的最小距离就跳出。
代码：

#include<iostream>#include<cstdio>#include<algorithm>#include<map>#include<vector>#include<queue>#include<cstring>using namespace std;typedef pair<int, int> P;typedef long long LL;const int N = 4e3+10;const int INF = 0x3f3f3f3f;struct edge{    int to, cost;};int V, min_;vector<edge> G[2*N];int d[N*2+1];void dijkstra(int s, int t){    priority_queue<P, vector<P>, greater<P> > que;    fill(d, d+V, INF);    d[s] = 0;    que.push(P(0,s));    while(!que.empty()){        P p = que.top(); que.pop();        int v = p.second;        if(d[v] < p.first) continue;        if(v == t) break;        if(d[v] >= min_) break;        for(int i = 0; i < (int)G[v].size(); i++){            edge e = G[v][i];            if(v == s && e.to == t) continue;            if(d[e.to] > d[v] + e.cost){                d[e.to] = d[v] + e.cost;                que.push(P(d[e.to], e.to));            }        }    }}map<P, int> mp;struct node{    int u, v, cost;}Eg[N];int main(){    int cas = 1, T, m;    cin >> T;    while(T--)    {        int cnt = 1;        scanf("%d", &m);        int cost, x1, y1, x2, y2;        for(int i = 1; i <= 2*N; i++) G[i].clear();        mp.clear();        for(int i = 1; i <= m; i++){            scanf("%d %d %d %d %d", &x1, &y1, &x2, &y2, &cost);            int u, v;            if(mp[P(x1, y1)] == 0){                mp[P(x1, y1)] = cnt++;            }            if(mp[P(x2,y2)] == 0){                mp[P(x2,y2)] = cnt++;            }            u = mp[P(x1,y1)], v = mp[P(x2,y2)];            G[u].push_back(edge{v,cost});            G[v].push_back(edge{u,cost});            Eg[i].cost = cost;            Eg[i].u = u;            Eg[i].v = v;        }        min_ = INF;        V = cnt;        for(int i = 1; i <= m; i++){            dijkstra(Eg[i].u, Eg[i].v);            min_ = min(min_, d[Eg[i].v] + Eg[i].cost);        }        if(min_ == INF){            printf("Case #%d: 0\n", cas++);        }        else           printf("Case #%d: %d\n", cas++, min_);    }    return 0;}

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