【SCOI2015】小凸玩矩阵

题面

https://www.luogu.org/problem/P4251

题解

// luogu-judger-enable-o2
#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>
#include<algorithm>
#define ri register int
#define N 300

using namespace std;

int read() {
  int ret=0,f=0; char ch=getchar();
  while (ch<'0' || ch>'9') f|=(ch=='-'),ch=getchar();
  while (ch>='0' && ch<='9') ret=ret*10+(ch-'0'),ch=getchar();
  return f?-ret:ret;
}

int n,m,k,tim,ans[N];
int va[N][N];
vector<int> to[N];
int vis[N],match[N];

bool dfs(int x) {
  for (ri i=0;i<to[x].size();i++) {
    int y=to[x][i];
    if (vis[y]==tim) continue;
    vis[y]=tim;
    if (!match[y] || dfs(match[y])) {
      match[y]=x;
      return 1;
    }
  }
  return 0;
}

int check(int x) {
  for (ri i=1;i<=n;i++) to[i].clear();
  memset(match,0,sizeof(match));
  memset(vis,0,sizeof(vis));
  for (ri i=1;i<=n;i++) 
    for (ri j=1;j<=m;j++) if (va[i][j]<=x) to[i].push_back(j);
  tim=0; int cnt=0;
  for (ri i=1;i<=n;i++) {
    ++tim;
    if (dfs(i)) cnt++;
  }
  return cnt;
}

int main() {
  
  n=read(); m=read(); k=read();
  k=n-k+1;
  for (ri i=1;i<=n;i++) 
    for (ri j=1;j<=m;j++) va[i][j]=read();
  int lb=0,rb=1e9;
  int ret=rb;
  while (lb<=rb) {
    int mid=(lb+rb)>>1;
    if (check(mid)>=k) ret=mid,rb=mid-1; else lb=mid+1;
  }
  printf("%d
",ret);
  return 0;
}