poj 2289 (最大流+二分)

题意：把n个好友分到m个组。求每个组的最大人数最小可以是多少人，，，

最大流+二分，，，，isap跑得还是挺快的，，，

#include<stdio.h>#include<string.h>const int N=1510;const int inf=0x3fffffff;int dis[N],gap[N],head[N],num,start,ans,end,first[N],nume,n,m;struct edge{int st,ed,flow,next;}E[510000];struct node{int x,next;}e[510000];void addedge(int x,int y,int w){E[num].st=x;E[num].ed=y;E[num].flow=w;E[num].next=head[x];head[x]=num++;E[num].st=y;E[num].ed=x;E[num].flow=0;E[num].next=head[y];head[y]=num++;}void Addedge(int x,int y){e[nume].x=y;e[nume].next=first[x];first[x]=nume++;}int dfs(int u,int minflow){if(u==end)return minflow;int i,v,f,flow=0,min_dis=ans-1;for(i=head[u];i!=-1;i=E[i].next){if(E[i].flow>0){v=E[i].ed;if(dis[v]+1==dis[u]){f=dfs(v,E[i].flow>minflow-flow?minflow-flow:E[i].flow);E[i].flow-=f;E[i^1].flow+=f;flow+=f;if(flow==minflow)break;if(dis[start]>=ans)return flow;}min_dis=min_dis>dis[v]?dis[v]:min_dis;}}if(flow==0){if(--gap[dis[u]]==0)   dis[start]=ans;dis[u]=min_dis+1;gap[dis[u]]++;}return flow;}int isap(){int maxflow=0;memset(dis,0,sizeof(dis));memset(gap,0,sizeof(gap));gap[0]=ans;while(dis[start]<ans)  maxflow+=dfs(start,inf);return maxflow;}void makemap(int D){memset(head,-1,sizeof(head));num=0;int i,j;for(i=1;i<=n;i++){addedge(start,i,1);for(j=first[i];j!=-1;j=e[j].next)    addedge(i,n+e[j].x,1);}for(i=1;i<=m;i++)addedge(i+n,end,D);}int main(){int i,j,k,flag,left,right,mid;char str[3000];while(scanf("%d%d",&n,&m),n||m){getchar();memset(first,-1,sizeof(first));nume=0;start=0;end=n+m+1;ans=end+1;for(i=1;i<=n;i++){gets(str);k=0;flag=0;for(j=0;str[j];j++){if(str[j]>='0'&&str[j]<='9'){k=k*10+str[j]-'0';flag=1;}else if(flag==1){Addedge(i,k+1);flag=0;k=0;}}if(flag==1) Addedge(i,k+1);}left=0;right=n;while(left<right){mid=(left+right)/2;//每个组最多的人数makemap(mid);if(isap()==n)  right=mid;else left=mid+1;}printf("%d\n",right);}return 0;}