POJ 1679 The Unique MST（次小生成树）

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////  main.cpp//  Richard////  Created by 邵金杰 on 16/8/18.//  Copyright © 2016年 邵金杰. All rights reserved.//#include<iostream>#include<cstdio>#include<vector>#include<cstring>#include<queue>using namespace std;const int maxn=100+5;const int INF=100000000;struct edge{    int u,v,w;    edge(int u,int v,int w): u(u),v(v),w(w) {}    bool operator < (const edge &e) const    {        return w>e.w;    }};int n,m;vector<vector<edge> > G(maxn);int vis[maxn],d[maxn][maxn],dist[maxn],map[maxn][maxn];void Prim(){    memset(vis,0,sizeof(vis));    memset(d,0,sizeof(d));    for(int i=1;i<=n;i++) dist[i]=INF;    priority_queue<edge> pq;    pq.push(edge(0,1,0));    edge nd(0,0,0);    int mst=0,cmst=INF;    while(!pq.empty())    {        do{            nd=pq.top();            pq.pop();        }while(vis[nd.v]&&!pq.empty());        if(vis[nd.v]==0)        {            map[nd.u][nd.v]=map[nd.v][nd.u]=0;            vis[nd.v]=1;            mst+=nd.w;            d[nd.u][nd.v]=nd.w;            for(int i=1;i<=n;i++)            {                if(vis[i])                {                    d[i][nd.v]=max(d[i][nd.u],d[nd.u][nd.v]);                    d[nd.v][i]=d[i][nd.v];                }            }            for(int i=0;i<G[nd.v].size();i++)            {                int e=G[nd.v][i].v;                if(!vis[e])                {                    int w=G[nd.v][i].w;                    if(dist[e]>w)                    {                        dist[e]=w;                        pq.push(edge(nd.v,e,w));                    }                }            }        }    }    for(int i=1;i<=n;i++)    {        for(int j=i+1;j<=n;j++)        {            if(map[i][j]) cmst=min(cmst,mst+map[i][j]-d[i][j]);        }    }    if(mst==cmst) printf("Not Unique!\n");    else printf("%d\n",mst);}int main(){    int t;    scanf("%d",&t);    while(t--)    {        memset(map,0,sizeof(map));        int a,b,c;        scanf("%d%d",&n,&m);        for(int i=1;i<=n;i++)            G[i].clear();        for(int i=0;i<m;i++)        {            scanf("%d%d%d",&a,&b,&c);            map[a][b]=map[b][a]=c;            G[a].push_back(edge(a,b,c));            G[b].push_back(edge(b,a,c));        }        Prim();    }}
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