hdu 3416 spfa+sap

来源：互联网发布：公需课挂机软件编辑：程序博客网时间：2024/06/13 21:45
1.spfa计算出最短路
2.如果是最短路上的边的话 uv之间建一条容量为1的边 dist[v]=dist[u]+cost[u][v]就能说明uv是最短路上的一条边
3.跑一边sap
#include<cstdio>#include<cstring>#include<algorithm>#include<vector>#include<queue>using namespace std;const int MAXN=2222;const int MAXM=333333;const int inf=1<<30;struct Edge{    int v,cap,next;}edge[MAXM];int head[MAXN],pre[MAXN],cur[MAXN],level[MAXN],gap[MAXN];int NE,NV,n,m;void init(){    NE=0;    memset(head,-1,sizeof(head));}void add(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++;}int SAP(int vs,int vt,int NV){    memset(pre,-1,sizeof(pre));    memset(level,0,sizeof(level));    memset(gap,0,sizeof(gap));    for(int i=0;i<NV;i++)cur[i]=head[i];    int u=pre[vs]=vs,maxflow=0,aug=-1;    gap[0]=NV;    while(level[vs]<NV){loop:        for(int &i=cur[u];i!=-1;i=edge[i].next){            int v=edge[i].v;            if(edge[i].cap&&level[u]==level[v]+1){                aug==-1?aug=edge[i].cap:aug=min(aug,edge[i].cap);                pre[v]=u;                u=v;                if(v==vt){                    maxflow+=aug;                    for(u=pre[u];v!=vs;v=u,u=pre[u]){                        edge[cur[u]].cap-=aug;                        edge[cur[u]^1].cap+=aug;                    }                    aug=-1;                }                goto loop;            }        }        int minlevel=NV;        for(int i=head[u];i!=-1;i=edge[i].next){            int v=edge[i].v;            if(edge[i].cap&&minlevel>level[v]){                cur[u]=i;                minlevel=level[v];            }        }        gap[level[u]]--;        if(gap[level[u]]==0)break;        level[u]=minlevel+1;        gap[level[u]]++;        u=pre[u];    }    return maxflow;}struct Node{    int v,cap;};vector<Node>vet[MAXN];int dist[MAXN];bool vis[MAXN];void spfa(int vs,int vt){    memset(vis,0,sizeof(vis));    for(int i=1;i<=n;i++) dist[i]=inf;    dist[vs]=0;    queue<int>q;    q.push(vs);    while(!q.empty())    {        int u=q.front();        q.pop();        vis[u]=false;        for(int i=0;i<vet[u].size();i++)        {            int v=vet[u][i].v;            int w=vet[u][i].cap;            if(dist[u]+w<dist[v])            {                dist[v]=dist[u]+w;                if(!vis[v])                {                    vis[v]=1;                    q.push(v);                }            }        }    }}int main(){    //freopen("C:\\Users\\Administrator\\Desktop\\input.txt","r",stdin);    int T,u,v,d,vs,vt;    scanf("%d",&T);    while(T--)    {        scanf("%d%d",&n,&m);        for(int i=1;i<=n;i++) vet[i].clear();        for(int i=1;i<=m;i++)        {            scanf("%d%d%d",&u,&v,&d);            if(u==v) continue;            Node p;            p.v=v,p.cap=d;            vet[u].push_back(p);        }        scanf("%d%d",&vs,&vt);        spfa(vs,vt);        NE=0,NV=n;        memset(head,-1,sizeof(head));        for(int i=1;i<=n;i++)        {            for(int j=0;j<vet[i].size();j++)            {                if(dist[vet[i][j].v]==dist[i]+vet[i][j].cap)                    add(i,vet[i][j].v,1);            }        }        printf("%d\n",SAP(vs,vt,NV));    }    return 0;}
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