POJ 1273 第一个SAP（ISAP）

/* sap学了很长时间，一直不敢下手写，结果就是不写永远不会真正的理解算法的含义，sap理论很多算法书上都有讲解，但我还是建议看数学专业 图论的书，比如 《有向图的理论，算法及应用》，这本书的内容非常棒，相信看过的都知道吧，比其他算法书上讲的透多了。
SAP有个优化就是 当出现断链时，就可以直接退出，还有个优化是当前弧的优化，这两个优化只需要一句话+一个数组就解决了，相当实惠，好的ISAP执行的效率真的非常高，我写的ISAP用的是链式前向星法表示。
这个就算是模板了吧，虽然写的不是很好。。*/

 

#include<iostream>

#include<cstdio>

#include<memory.h>

#include<cmath>

using namespace std;



#define MAXN 500

#define MAXE 40000

#define INF 0x7fffffff



long ne,nv,tmp,s,t,index;



struct Edge{

    long next,pair;

    long v,cap,flow;

}edge[MAXE];

long net[MAXN];

long ISAP()

{

    long numb[MAXN],dist[MAXN],curedge[MAXN],pre[MAXN];

    long cur_flow,max_flow,u,tmp,neck,i;

    memset(dist,0,sizeof(dist));

    memset(numb,0,sizeof(numb));

    memset(pre,-1,sizeof(pre));

    for(i = 1 ; i <= nv ; ++i)

        curedge[i] = net[i];

    numb[nv] = nv;

    max_flow = 0;

    u = s;

    while(dist[s] < nv)

    {

        /* first , check if has augmemt flow */

        if(u == t)

        {

            cur_flow = INF;

            for(i = s; i != t;i = edge[curedge[i]].v) 

            {  

                if(cur_flow > edge[curedge[i]].cap)

                {

                    neck = i;

                    cur_flow = edge[curedge[i]].cap;

                }

            }

            for(i = s; i != t; i = edge[curedge[i]].v)

            {

                tmp = curedge[i];

                edge[tmp].cap -= cur_flow;

                edge[tmp].flow += cur_flow;

                tmp = edge[tmp].pair;

                edge[tmp].cap += cur_flow;

                edge[tmp].flow -= cur_flow;

            }

            max_flow += cur_flow;

            u = neck;

        }

        /* if .... else ... */

        for(i = curedge[u]; i != -1; i = edge[i].next)

            if(edge[i].cap > 0 && dist[u] == dist[edge[i].v]+1)

                break;

        if(i != -1)

        {

            curedge[u] = i;

            pre[edge[i].v] = u;

            u = edge[i].v;

        }else{

            if(0 == --numb[dist[u]]) break;

            curedge[u] = net[u];

            for(tmp = nv,i = net[u]; i != -1; i = edge[i].next)

                if(edge[i].cap > 0)

                    tmp = tmp<dist[edge[i].v]?tmp:dist[edge[i].v];

            dist[u] = tmp + 1;

            ++numb[dist[u]];

            if(u != s) u = pre[u];

        }

    }

    

    return max_flow;

}

int main() {

    long i,j,np,nc,m,n;

    long a,b,val;

    long g[MAXN][MAXN];

    while(scanf("%d%d",&ne,&nv)!=EOF)

    {

        s = 1;

        t = nv;

        memset(g,0,sizeof(g));

        memset(net,-1,sizeof(net));

        for(i=0;i<ne;++i)

        {

            scanf("%ld%ld%ld",&a,&b,&val);

            g[a][b] += val;

         }

         for(i=1;i<=nv;++i)

             for(j = i; j <= nv;++j)

                 if(g[i][j]||g[j][i])

                 {

                     edge[index].next = net[i];

                     edge[index].v = j;

                     edge[index].cap = g[i][j];

                     edge[index].flow = 0;

                     edge[index].pair = index+1;

                     net[i] = index++;

                     edge[index].next = net[j];

                     edge[index].v = i;

                     edge[index].cap = g[j][i];

                     edge[index].flow = 0;

                     edge[index].pair = index-1;

                     net[j] = index++;

                 }

        printf("%ld\n",ISAP());

    }

    return 0;

}