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;
}
补充：软件开发 , C++ ,
