ISAP 模板

Posted 2020-06-17

  1 #include <iostream>
  2 #include <cstring>
  3 #include <cstdio>
  4 #include <queue>
  5 
  6 using namespace std;
  7 const int INF=2147483647;
  8 const int maxn=210,maxm=410;
  9 int cnt,fir[maxn],nxt[maxm],cap[maxm],to[maxm],dis[maxn],gap[maxn],path[maxn];
 10 
 11 void addedge(int a,int b,int c)
 12 {
 13     nxt[++cnt]=fir[a];
 14     to[cnt]=b;
 15     cap[cnt]=c;
 16     fir[a]=cnt;
 17 }
 18 
 19 bool BFS(int S,int T)
 20 {
 21     memset(dis,0,sizeof(dis));
 22     dis[T]=1;
 23     queue<int>q;q.push(T);
 24     while(!q.empty())
 25     {
 26         int node=q.front();q.pop();
 27         for(int i=fir[node];i;i=nxt[i])
 28         {
 29             if(dis[to[i]])continue;
 30             dis[to[i]]=dis[node]+1;
 31             q.push(to[i]);
 32         }
 33     }
 34     return dis[S];
 35 }
 36 int fron[maxn];
 37 int ISAP(int S,int T)
 38 {
 39     if(!BFS(S,T))
 40         return 0;
 41     for(int i=1;i<=T;i++)++gap[dis[i]];
 42     int p=S,ret=0;
 43     memcpy(fron,fir,sizeof(fir));
 44     while(dis[S]<=T)
 45     {
 46         if(p==T){
 47             int f=INF;
 48             while(p!=S){
 49                 f=min(f,cap[path[p]]);
 50                 p=to[path[p]^1];
 51             }
 52             p=T;ret+=f;
 53             while(p!=S){
 54                 cap[path[p]]-=f;
 55                 cap[path[p]^1]+=f;
 56                 p=to[path[p]^1];
 57             }
 58         }
 59         int &ii=fron[p];
 60         for(;ii;ii=nxt[ii]){
 61             if(!cap[ii]||dis[to[ii]]+1!=dis[p])
 62                 continue;
 63             else 
 64                 break;
 65         }
 66                 
 67         if(ii){
 68             p=to[ii];
 69             path[p]=ii;
 70         }
 71             
 72         
 73         else{
 74             if(--gap[dis[p]]==0)break;
 75             int minn=T+1;
 76             for(int i=fir[p];i;i=nxt[i])
 77                 if(cap[i])
 78                     minn=min(minn,dis[to[i]]);
 79             gap[dis[p]=minn+1]++;
 80             fron[p]=fir[p];
 81             if(p!=S)
 82                 p=to[path[p]^1];        
 83         }
 84     }
 85     return ret;
 86 }
 87 
 88 void Init()
 89 {
 90     memset(fir,0,sizeof(fir));
 91     cnt=1;
 92 }
 93 int main()
 94 {
 95     int n,m;
 96     while(~scanf("%d%d",&m,&n))
 97     {
 98         Init();
 99         for(int i=1;i<=m;i++){
100             int x,y,c;
101             scanf("%d%d%d",&x,&y,&c);
102             addedge(x,y,c);
103             addedge(y,x,0);
104         }
105         printf("%d\n",ISAP(1,n));
106     }
107 
108     return 0;
109 }