【BZOJ4883】棋盘上的守卫

题面

http://darkbzoj.tk/problem/4883

题解

克鲁斯卡尔维护基环森林。

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#define ri register int
#define N 100050
using namespace std;

struct edge {
  int u,v,l;
  bool operator < (const edge &rhs) const {
    return l<rhs.l;
  }
} e[N];
int n,m;
int cir[N<<1];
int f[N<<1];

int findroot(int x){
  if (f[x]==x) return x;
  return f[x]=findroot(f[x]);
}

int main() {
  int c;
  int tt=0;
  scanf("%d %d",&n,&m);
  for (ri i=1;i<=n;i++) 
    for (ri j=1;j<=m;j++) {
      scanf("%d",&c);
      e[++tt]=(edge){i,j+n,c};
    }
  sort(e+1,e+tt+1);
  long long ans=0;
  for (ri i=1;i<=n+m;i++) f[i]=i;
  for (ri i=1;i<=tt;i++) {
    int r1=findroot(e[i].u),r2=findroot(e[i].v);
    if (cir[r1] && cir[r2]) continue;
    if (r1==r2) {
      cir[r1]=1;
      ans+=e[i].l;
      continue;
    }
    f[r2]=r1;cir[r1]|=cir[r2];
    ans+=e[i].l;
  }
  cout<<ans<<endl;
}