poj 1273 最大流 ford-fulkerson

#include <iostream>#include <cstdio>#include <queue>#include <cstring>using namespace std;#define MAXN 210struct Matrix{  int c,f;     //容量，流量};int M,N;Matrix Edge[MAXN][MAXN];   //流网络int s,t;int residual[MAXN][MAXN];   //残留网络int qu[MAXN*MAXN],qs,qe;   //队列int pre[MAXN];             //记录增广路的前一个节点int vis[MAXN];             //标记增广路int maxflow,min_augment;   //最大流，可改进量void find_augment_path()   //BFS寻找增广路{  int i,cu;  memset(vis,0,sizeof(vis));  //  memset(pre,0,sizeof(pre));  qs = 0;  qu[qs] = s;  pre[s] = s;  vis[s] = 1;  qe = 1;  memset(residual,0,sizeof(residual));  memset(pre,0,sizeof(pre));  while(qs < qe && pre[t] == 0)    {      cu = qu[qs];      for(int i = 1; i <= N; i++){  if(vis[i] == 0)    {      if(Edge[cu][i].c - Edge[cu][i].f > 0){  residual[cu][i] = Edge[cu][i].c - Edge[cu][i].f;  pre[i] = cu; qu[qe++] = i; vis[i] = 1;}      else if(Edge[i][cu].f > 0){  residual[cu][i] = Edge[i][cu].f;  pre[i] = cu; qu[qe++] = i; vis[i] = 1;}    }}      qs++;    }}void augment_flow()    //计算改进量{  int i = t,j;  if(pre[i] == 0)  //如果不存在增广路    {      min_augment = 0;      return;    }  j = 0x7fffffff;   //设置j为无穷大  while(i != s)      //倒向追踪    {      if(residual[pre[i]][i] < j)   //如果存在残留网络{  j = residual[pre[i]][i];   //计算增广路上最小残留值即为改进量}      i = pre[i];      }  min_augment = j;}void update_flow()    //更新网络流{  int i = t;  if(pre[i] == 0)   //如果没有增广路    return;  while(i != s)    {      if(Edge[pre[i]][i].c - Edge[pre[i]][i].f > 0){  Edge[pre[i]][i].f += min_augment;}      else if(Edge[i][pre[i]].f > 0){  Edge[pre[i]][i].f -= min_augment;}      i = pre[i];    }}void Ford()     //增广路算法{  s = 1; t = N;  maxflow = 0;  while(1)    {      find_augment_path();      augment_flow();      maxflow += min_augment;      if(min_augment > 0)    //如果有增广路update_flow();      else              //如果没有增广路return;    }}int main(){  int i;  int u,v,c;  while(scanf("%d%d",&M,&N) != EOF)    {      memset(Edge,0,sizeof(Edge));      for(i = 0; i < M; i++){  cin>>u>>v>>c;  Edge[u][v].c += c;}      Ford();      cout<<maxflow<<endl;    }  return 0;}