poj 3469(网络流模版)

题目链接：http://poj.org/problem?id=3469

思路：终于把网络流的模版测试好了，在Dinic和Sap之间还是选择了Sap,事实证明Sap确实比Dinic效率高，在此贴出自己的网络流模版：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
#define MAXN 44444
#define MAXM 999999
#define inf 1<<30

struct Edge {
    int v,cap,next;
} edge[MAXM];

int n,m,vs,vt,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++;
}

int level[MAXN];
int gap[MAXN];

void bfs(int vt)
{
    memset(level,-1,sizeof(level));
    memset(gap,0,sizeof(gap));
    level[vt]=0;
    gap[level[vt]]++;
    queue<int>que;
    que.push(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];
int 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,flow=0,aug=inf;
    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&&level[u]==level[v]+1) {
                flag=true;
                pre[v]=u;
                u=v;
                //  aug=(aug==-1?edge[i].cap:min(aug,edge[i].cap));
                aug=min(aug,edge[i].cap);
                if(v==vt) {
                    flow+=aug;
                    for(u=pre[v]; v!=vs; v=u,u=pre[u]) {
                        edge[cur[u]].cap-=aug;
                        edge[cur[u]^1].cap+=aug;
                    }
                    //     aug=-1;
                    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&&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 flow;
}


int main()
{
    int u,v,w,w1,w2;
    scanf("%d%d",&n,&m);
    vs=0;
    vt=n+1;
    NV=n+2;
    NE=0;
    memset(head,-1,sizeof(head));
    for(int i=1; i<=n; i++) {
        scanf("%d%d",&w1,&w2);
        Insert(vs,i,w1);
        Insert(i,vt,w2);
    }
    for(int i=1; i<=m; i++) {
        scanf("%d%d%d",&u,&v,&w);
        Insert(u,v,w);
        Insert(v,u,w);
    }
    printf("%d
",SAP(vs,vt));
    return 0;
}