HDU 3416 Marriage Match IV

最短路+最大流

#include<cstdio>
#include<cstring>
#include<string>
#include<cmath>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;

const int maxn=1000+10;
const int MAXN=100000+10;
const int INF=0x7FFFFFFF;

struct Edge
{
    int from,to,cap,flow;
};
vector<Edge>edges;
vector<int>G[maxn];
struct EE1
{
    int from,to,w;
} ee1[MAXN];
struct EE2
{
    int from,to,w;
} ee2[MAXN];
vector<EE1>SPFAG1[maxn];
vector<EE2>SPFAG2[maxn];
bool vis[maxn];
int d[maxn];
int cur[maxn];
int U[MAXN],V[MAXN],C[MAXN];
int FF1[maxn],Dis1[maxn],FF2[maxn],Dis2[maxn];
int n,m,s,t,N,M;

//求出层次网络
bool BFS()
{
    memset(vis,0,sizeof(vis));
    queue<int>Q;
    Q.push(s);
    d[s]=0;
    vis[s]=1;
    while(!Q.empty())
    {
        int x=Q.front();
        Q.pop();
        for(int i=0; i<G[x].size(); i++)
        {
            Edge& e=edges[G[x][i]];
            if(!vis[e.to]&&e.cap>e.flow)
            {
                vis[e.to]=1;
                d[e.to]=d[x]+1;
                Q.push(e.to);
            }
        }
    }
    return vis[t];
}

//加边
void AddEdge(int from,int to,int cap)
{
    Edge r;
    r.from=from;
    r.to=to;
    r.cap=cap;
    r.flow=0;
    edges.push_back(r);
    Edge d;
    d.from=to;
    d.to=from;
    d.cap=0;
    d.flow=0;
    edges.push_back(d);
    m=edges.size();
    G[from].push_back(m-2);
    G[to].push_back(m-1);
}

//每个阶段来一次DFS增广
int DFS(int x,int a)
{
    if(x==t||a==0) return a;
    int flow=0,f;
    for(int i=cur[x]; i<G[x].size(); i++)
    {
        Edge& e=edges[G[x][i]];
        if(d[x]+1==d[e.to]&&(f=DFS(e.to,min(a,e.cap-e.flow)))>0)
        {
            e.flow+=f;
            edges[G[x][i]^1].flow-=f;
            flow+=f;
            a-=f;
            if(a==0) break;
        }
    }
    return flow;
}

//多个阶段，多次建立层次网络。
int Maxflow(int ss,int tt)
{
    int flow=0;
    while(BFS())
    {
        memset(cur,0,sizeof(cur));
        flow+=DFS(ss,INF);
    }
    return flow;
}

void SPFA1()
{
    for(int i=0; i<=N; i++) Dis1[i]=INF;
    queue<int>Q;
    Q.push(s);
    FF1[s]=1;
    Dis1[s]=0;
    while(!Q.empty())
    {
        int h=Q.front();
        Q.pop();
        FF1[h]=0;
        for(int i=0; i<SPFAG1[h].size(); i++)
        {
            EE1 edge=SPFAG1[h][i];
            if(Dis1[h]+edge.w<Dis1[edge.to])
            {
                Dis1[edge.to]=Dis1[h]+edge.w;
                if(FF1[edge.to]==0)
                {
                    FF1[edge.to]=1;
                    Q.push(edge.to);
                }
            }
        }
    }
}

void SPFA2()
{
    for(int i=0; i<=N; i++) Dis2[i]=INF;
    queue<int>Q;
    Q.push(t);
    FF2[t]=1;
    Dis2[t]=0;
    while(!Q.empty())
    {
        int h=Q.front();
        Q.pop();
        FF2[h]=0;
        for(int i=0; i<SPFAG2[h].size(); i++)
        {
            EE2 edge=SPFAG2[h][i];
            if(Dis2[h]+edge.w<Dis2[edge.to])
            {
                Dis2[edge.to]=Dis2[h]+edge.w;
                if(FF2[edge.to]==0)
                {
                    FF2[edge.to]=1;
                    Q.push(edge.to);
                }
            }
        }
    }
}

int main()
{
    int TT;
    scanf("%d",&TT);
    while(TT--)
    {
        scanf("%d%d",&N,&M);
        edges.clear();
        for(int i=0; i<maxn; i++) G[i].clear();
        for(int i=0; i<maxn; i++) SPFAG1[i].clear();
        for(int i=0; i<maxn; i++) SPFAG2[i].clear();
        for(int i=1; i<=M; i++)
        {
            scanf("%d%d%d",&U[i],&V[i],&C[i]);
            ee1[i].from=U[i];
            ee1[i].to=V[i];
            ee1[i].w=C[i];
            ee2[i].from=V[i];
            ee2[i].to=U[i];
            ee2[i].w=C[i];
            SPFAG1[U[i]].push_back(ee1[i]);
            SPFAG2[V[i]].push_back(ee2[i]);
        }
        scanf("%d%d",&s,&t);
        SPFA1();SPFA2();
        for(int i=1; i<=M; i++)
            if(Dis1[U[i]]+Dis2[V[i]]+C[i]==Dis1[t])
                AddEdge(U[i],V[i],1);
        printf("%d
",Maxflow(s,t));
    }
    return 0;
}