poj 3469(网络流模版)

来源：互联网发布：mac php protobuf 编辑：程序博客网时间：2024/06/08 17:12

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：

  1 #include<iostream>  2 #include<cstdio>  3 #include<cstring>  4 #include<algorithm>  5 #include<queue>  6 using namespace std;  7 #define MAXN 44444  8 #define MAXM 999999  9 #define inf 1<<30 10  11 struct Edge { 12     int v,cap,next; 13 } edge[MAXM]; 14  15 int n,m,vs,vt,NE,NV; 16 int head[MAXN]; 17  18 void Insert(int u,int v,int cap) 19 { 20     edge[NE].v=v; 21     edge[NE].cap=cap; 22     edge[NE].next=head[u]; 23     head[u]=NE++; 24  25     edge[NE].v=u; 26     edge[NE].cap=0; 27     edge[NE].next=head[v]; 28     head[v]=NE++; 29 } 30  31 int level[MAXN]; 32 int gap[MAXN]; 33  34 void bfs(int vt) 35 { 36     memset(level,-1,sizeof(level)); 37     memset(gap,0,sizeof(gap)); 38     level[vt]=0; 39     gap[level[vt]]++; 40     queue<int>que; 41     que.push(vt); 42     while(!que.empty()) { 43         int u=que.front(); 44         que.pop(); 45         for(int i=head[u]; i!=-1; i=edge[i].next) { 46             int v=edge[i].v; 47             if(level[v]!=-1)continue; 48             level[v]=level[u]+1; 49             gap[level[v]]++; 50             que.push(v); 51  52         } 53     } 54 } 55  56  57 int pre[MAXN]; 58 int cur[MAXN]; 59  60 int SAP(int vs,int vt) 61 { 62     bfs(vt); 63     memset(pre,-1,sizeof(pre)); 64     memcpy(cur,head,sizeof(head)); 65     int u=pre[vs]=vs,flow=0,aug=inf; 66     gap[0]=NV; 67     while(level[vs]<NV) { 68         bool flag=false; 69         for(int &i=cur[u]; i!=-1; i=edge[i].next) { 70             int v=edge[i].v; 71             if(edge[i].cap&&level[u]==level[v]+1) { 72                 flag=true; 73                 pre[v]=u; 74                 u=v; 75                 //  aug=(aug==-1?edge[i].cap:min(aug,edge[i].cap)); 76                 aug=min(aug,edge[i].cap); 77                 if(v==vt) { 78                     flow+=aug; 79                     for(u=pre[v]; v!=vs; v=u,u=pre[u]) { 80                         edge[cur[u]].cap-=aug; 81                         edge[cur[u]^1].cap+=aug; 82                     } 83                     //     aug=-1; 84                     aug=inf; 85                 } 86                 break; 87             } 88         } 89         if(flag)continue; 90         int minlevel=NV; 91         for(int i=head[u]; i!=-1; i=edge[i].next) { 92             int v=edge[i].v; 93             if(edge[i].cap&&level[v]<minlevel) { 94                 minlevel=level[v]; 95                 cur[u]=i; 96             } 97         } 98         if(--gap[level[u]]==0)break; 99         level[u]=minlevel+1;100         gap[level[u]]++;101         u=pre[u];102     }103     return flow;104 }105 106 107 int main()108 {109     int u,v,w,w1,w2;110     scanf("%d%d",&n,&m);111     vs=0;112     vt=n+1;113     NV=n+2;114     NE=0;115     memset(head,-1,sizeof(head));116     for(int i=1; i<=n; i++) {117         scanf("%d%d",&w1,&w2);118         Insert(vs,i,w1);119         Insert(i,vt,w2);120     }121     for(int i=1; i<=m; i++) {122         scanf("%d%d%d",&u,&v,&w);123         Insert(u,v,w);124         Insert(v,u,w);125     }126     printf("%d\n",SAP(vs,vt));127     return 0;128 }

View Code

0 0