BZOJ1191: [HNOI2006]超级英雄Hero

这题标解是改一下匈牙利算法，显然，像我这种从不用匈牙利的人，会找个办法用网络流…

具体做法是这样，二分最后的答案ans，然后对前ans个问题建图跑网络流，看最大流能不能到ans。

 /**************************************************************
     Problem: 1191
     User: zhuohan123
     Language: C++
     Result: Accepted
     Time:64 ms
     Memory:3128 kb
 ****************************************************************/

 #include <iostream>
 #include <cstdio>
 #include <queue>
 #include <algorithm>
 #include <cstring>
 using namespace std;
 int head[],pointsize;
 struct edge{int to,next,c,p;};
 edge g[];int gnum=;
 void addedge(int from,int to,int c)
 {
     g[++gnum].to=to;g[gnum].c=c;g[gnum].next=head[from];head[from]=gnum;
     g[++gnum].to=from;g[gnum].c=;g[gnum].next=head[to];head[to]=gnum;
 }
 int dfsstart,dfsend,ans;
 bool haveans;int dfsans;
 int d[],vd[];
 void dfs(int po)
 {
     if(po==dfsend)
     {
         ans+=dfsans;
         haveans=true;
         return ;
     }
     int mind=pointsize-,tempans=dfsans;
     for(int i=head[po];i;i=g[i].next)
     if(g[i].c)
     {
         if(d[g[i].to]+==d[po])
         {
             if(g[i].c<dfsans)dfsans=g[i].c;
             dfs(g[i].to);
             if(d[dfsstart]>=pointsize)return ;
             if(haveans)
             {
                 g[i].c-=dfsans;
                 g[i^].c+=dfsans;
                 return ;
             }
             dfsans=tempans;
         }
         if(d[g[i].to]<mind)mind=d[g[i].to];
     }
     vd[d[po]]--;
     if(!vd[d[po]])d[dfsstart]=pointsize;
     d[po]=mind+;vd[d[po]]++;
 }
 int isap(int start,int end)
 {
     ans=;
     memset(d,,sizeof(d));
     memset(vd,,sizeof(vd));
     vd[]=pointsize;
     dfsstart=start;
     dfsend=end;
     while(d[dfsstart]<pointsize)
     {
         dfsans=;
         haveans=false;
         dfs(dfsstart);
     }
     return ans;
 }
 int n,m;
 int mj[][];
 bool check(int po)
 {
     gnum=;memset(head,,sizeof(head));
     for(int i=;i<=n;i++)addedge(n+m+,i,);
     for(int i=;i<=po;i++)addedge(i+n,n+m+,);
     pointsize=n+m+;
     for(int i=;i<=po;i++)
     {
         addedge(mj[i][]+,i+n,);
         addedge(mj[i][]+,i+n,);
     }
     return po==isap(n+m+,n+m+);
 }
 int imerge(int l,int r)
 {
     if(l==r)return l;
     int mid=(l+r)/+;
     if(check(mid))return imerge(mid,r);
     else return imerge(l,mid-);
 }
 int main(int argc ,char *argv[])
 {
     scanf("%d%d",&n,&m);
     for(int i=;i<=m;i++)scanf("%d%d",&mj[i][],&mj[i][]);
     printf("%d\n",imerge(,m));
     return ;
 }