tjut 3599

来源：互联网发布：优酷有电视版软件编辑：程序博客网时间：2024/06/05 09:20
#include<iostream>#include<cstdio>#include<string>#include<algorithm>#include<vector>#include<queue>using namespace std;#define MAXN 4444#define inf 1<<30struct Node{    int v,w;    Node(int vv,int ww):v(vv),w(ww){};};int n;bool mark[MAXN];int dist[MAXN];vector<vector<Node> >G;void spfa(){    memset(mark,false,sizeof(mark));    fill(dist,dist+n+2,inf);    dist[1]=0;    queue<int>que;    que.push(1);    while(!que.empty()){        int u=que.front();        que.pop();        mark[u]=false;        for(int i=0;i<G[u].size();i++){            int v=G[u][i].v;            int w=G[u][i].w;            if(dist[u]+w<dist[v]){                dist[v]=dist[u]+w;                if(!mark[v]){                    mark[v]=true;                    que.push(v);                }            }        }    }}struct Edge{    int v,cap,next;}edge[MAXN*MAXN];int NE,NV;int head[MAXN];void Insert(int u,int v,int cap){    edge[NE].v=v;    edge[NE].cap=cap;    edge[NE].next=head[u];    head[u]=NE++;    edge[NE].v=u;    edge[NE].cap=0;    edge[NE].next=head[v];    head[v]=NE++;}void Build(){    NE=0;    NV=n;    memset(head,-1,sizeof(head));    for(int u=1;u<=n;u++){        for(int i=0;i<G[u].size();i++){            int v=G[u][i].v,w=G[u][i].w;            if(dist[u]+w==dist[v]){                Insert(u,v,1);            }        }    }}int level[MAXN],gap[MAXN];void bfs(int vt){    memset(level,-1,sizeof(level));    memset(gap,0,sizeof(gap));    queue<int>que;    que.push(vt);    level[vt]=0;    gap[level[vt]]++;    while(!que.empty()){        int u=que.front();        que.pop();        for(int i=head[u];i!=-1;i=edge[i].next){            int v=edge[i].v;            if(level[v]!=-1)continue;            level[v]=level[u]+1;            gap[level[v]]++;            que.push(v);        }    }}int pre[MAXN],cur[MAXN];int SAP(int vs,int vt){    bfs(vt);    memset(pre,-1,sizeof(pre));    memcpy(cur,head,sizeof(head));    int u=pre[vs]=vs,aug=inf,maxflow=0;    gap[0]=NV;    while(level[vs]<NV){        bool flag=false;        for(int &i=cur[u];i!=-1;i=edge[i].next){            int v=edge[i].v;            if(edge[i].cap>0&&level[u]==level[v]+1){                flag=true;                aug=min(aug,edge[i].cap);                pre[v]=u;                u=v;                if(v==vt){                    maxflow+=aug;                    for(u=pre[v];v!=vs;v=u,u=pre[u]){                        edge[cur[u]].cap-=aug;                        edge[cur[u]^1].cap+=aug;                    }                    aug=inf;                }                break;            }        }        if(flag)continue;        int minlevel=NV;        for(int i=head[u];i!=-1;i=edge[i].next){            int v=edge[i].v;            if(edge[i].cap>0&&level[v]<minlevel){                minlevel=level[v];                cur[u]=i;            }        }        if(--gap[level[u]]==0)break;        level[u]=minlevel+1;        gap[level[u]]++;        u=pre[u];    }    return maxflow;}int main(){    int _case,u,v,w;    scanf("%d",&_case);    while(_case--){        scanf("%d",&n);        G.clear();        G.resize(n+2);        while(true){            scanf("%d%d%d",&u,&v,&w);            if(u==0&&v==0&&w==0)break;            G[u].push_back(Node(v,w));            G[v].push_back(Node(u,w));        }        spfa();        if(dist[n]==inf||n==1){            puts("0");            continue;        }        Build();        printf("%d\n",SAP(1,n));    }    return 0;}
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