最大流(Isap模板)

http://acm.hdu.edu.cn/showproblem.php?pid=1532

  1 #include <iostream>

  2 #include <cstdio>

  3 #include <climits>

  4 #include <cstring>

  5 #include <algorithm>

  6 using namespace std;

  7 typedef  struct {int v,next,val;} edge;

  8 const int MAXN=20010;

  9 const int MAXM=500010;

 10 edge e[MAXM];

 11 int p[MAXN],eid;

 12 inline void init(){memset(p,-1,sizeof(p));eid=0;}

 13 //有向

 14 inline void insert1(int from,int to,int val)

 15 {

 16     e[eid].v=to;e[eid].val=val;

 17     e[eid].next=p[from];

 18     p[from]=eid++;

 19     swap(from,to);

 20     e[eid].v=to;e[eid].val=0;

 21     e[eid].next=p[from];

 22     p[from]=eid++;

 23 }

 24 //无向

 25 inline void insert2(int from,int to,int val)

 26 {

 27     e[eid].v=to;e[eid].val=val;

 28     e[eid].next=p[from];

 29     p[from]=eid++;

 30     swap(from,to);

 31     e[eid].v=to;e[eid].val=val;

 32     e[eid].next=p[from];

 33     p[from]=eid++;

 34 }

 35 int n,m;//n为点数 m为边数

 36 int h[MAXN];

 37 int gap[MAXN];

 38 int source,sink;

 39 inline int dfs(int pos,int cost)

 40 {

 41     if (pos==sink) return cost;

 42 

 43     int j,minh=n-1,lv=cost,d;

 44     for (j=p[pos];j!=-1;j=e[j].next)

 45     {

 46         int v=e[j].v,val=e[j].val;

 47         if(val>0)

 48         {

 49             if (h[v]+1==h[pos])

 50             {

 51                 if (lv<e[j].val) d=lv;

 52                 else d=e[j].val;

 53 

 54                 d=dfs(v,d);

 55                 e[j].val-=d;

 56                 e[j^1].val+=d;

 57                 lv-=d;

 58                 if (h[source]>=n) return cost-lv;

 59                 if (lv==0) break;

 60             }

 61             if (h[v]<minh)    minh=h[v];

 62         }

 63     }

 64     if (lv==cost)

 65     {

 66         --gap[h[pos]];

 67         if (gap[h[pos]]==0) h[source]=n;

 68         h[pos]=minh+1;

 69         ++gap[h[pos]];

 70     }

 71     return cost-lv;

 72 }

 73 

 74 int isap(int st,int ed)

 75 {

 76 

 77     source=st;sink=ed;

 78     int ret=0;

 79     memset(gap,0,sizeof(gap));

 80     memset(h,0,sizeof(h));

 81     gap[st]=n;

 82     while (h[st]<n)

 83     {

 84         ret+=dfs(st,INT_MAX);

 85     }

 86     return ret;

 87 }

 88 int main()

 89 {

 90     while(cin>>m>>n)

 91     {

 92         init();

 93         for(int i=0;i<m;i++)

 94         {

 95             int u,v,c;

 96             scanf("%d%d%d",&u,&v,&c);

 97             insert1(u,v,c);

 98         }

 99         printf("%d\n",isap(1,n));

100     }

101     return 0;

102 }