poj1273 最大流

用的是EdmondsKarp

程序可以再优化的，懒得优化了

EdmondsKarp

#include <iostream>#include<stdio.h>#include <queue>#include <limits>#include <cstring>using namespace std;const int maxNode = 202;int N = 201;//edgeint M = 201;//nodeconst int maxInt = numeric_limits<int>::max();int g[maxNode][maxNode];int f[maxNode][maxNode];int residual[maxNode][maxNode];int pre[maxNode];bool BFS(){queue<int> q;q.push(1);memset(pre,0,sizeof(int)*(M+1));int used[maxNode];memset(used,0,sizeof(int)*(M+1));used[1] = 1;while (!q.empty()){int curr = q.front();q.pop();for (int i=1;i<=M;++i){if(residual[curr][i]>0 && !used[i]){pre[i] = curr;if(i==M)return true;q.push(i);used[i] = 1;}}}return false;}void EdmondsKarp(){while (BFS()){int minF = maxInt;int curr = M;int beg=0,end = 0;while (curr!=1){int preNode = pre[curr];if(minF > residual[preNode][curr]){minF = residual[preNode][curr];beg = preNode;end = curr;}curr = preNode;}curr = M;while (curr != 1){int preNode = pre[curr];f[preNode][curr] +=minF;residual[preNode][curr] -=minF;residual[curr][preNode] = f[preNode][curr];curr = preNode;}}int sum=0;for (int i=1;i<M;++i){sum +=f[i][M];}cout<< sum<<endl;}int main(){while(scanf("%d%d",&N,&M)!=EOF){for (int i=1;i<=M;++i){memset(g[i],0,sizeof(int)*(M+1));memset(f[i],0,sizeof(int)*(M+1));memset(residual[i],0,sizeof(int)*(M+1));}for (int i=0;i<N;++i){int start,end,capacity;scanf("%d%d%d",&start,&end,&capacity);g[start][end] += capacity;//这个地方太坑爹了，不是最大的容量吗，为毛要加呢residual[start][end] += capacity;}/*for (int i=1;i<=M;++i){for(int j=1;j<=M;++j)cout<<g[i][j]<<" ";cout<<endl;}*/EdmondsKarp();}return 0;}

下面是别人优化的比较好的

#include<iostream>#include<cstring>#include<queue>using namespace std;#define inf INT_MAXint n,m,a[205][205],pre[205];int bfs(){    queue<int>Q;    Q.push(1);    pre[1]=0;    memset(pre,-1,sizeof(pre));    int t,i;    while(!Q.empty())    {       t=Q.front();       Q.pop();       for(i=2;i<=n;i++)       if(pre[i]==-1&&a[t][i]>0)       {          pre[i]=t;          Q.push(i);          if(i==n)   return 1;       }    }    return -1;}int maxflow(){    int res=0,ans,t;    while(bfs()==1)    {       t=n;       ans=inf;       while(t!=1)       {           if(a[pre[t]][t]<ans)   ans=a[pre[t]][t];           t=pre[t];       }                  res=res+ans;       t=n;       while(t!=1)       {           a[pre[t]][t]-=ans;           a[t][pre[t]]+=ans;           t=pre[t];       }    }    return res;}int main(){     while(scanf("%d%d",&m,&n)!=EOF)     {          int i,j;          memset(a,0,sizeof(a));          for(i=0;i<m;i++)          {              int b,c,d;              scanf("%d%d%d",&b,&c,&d);              a[b][c]+=d;          }          printf("%d\n",maxflow());     }}

最大流效率更高的算法为：

Push-Relabel算法

Relabel-to-Front算法（http://cuitianyi.com/blog/%E6%B1%82%E6%9C%80%E5%A4%A7%E6%B5%81%E7%9A%84relabel-to-front%E7%AE%97%E6%B3%95/）

Preflow-Push算法

Dinic算法（可以参考国家集训队 2007 王欣上《浅谈基于分层思想的网络流算法》）