BZOJ4443[Scoi2015][小凸玩矩阵] 二分图最大匹配+二分

题目链接

题解：二分第K大的值，把小于这个值的边加入图中，再求最大匹配,看能不能找出n-k+1个数<=mid

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int N = 305 ;

int lk
, w

, vis
;
int n , m , mid , k ;

bool find ( int u ){
for ( int i = 1 ; i <= m ; ++ i )
if ( w [u] [i] <= mid && ! vis [i] ) {
vis [i] = 1 ;
if ( lk [i] == 0 || find ( lk [i] ) ){
lk [i] = u;
return true ;
}
}
return false ;
}

bool check (){
int ans = 0 ;
memset ( lk, 0 , sizeof ( lk ) );
for ( int i = 1 ; i <= n ; ++ i ){
memset ( vis , 0 , sizeof ( vis ) );
ans += find ( i ) ;
}
return ans > n - k ;
}

int main() {
scanf ( "%d%d%d", &n , &m , &k );
for ( int i = 1 ; i <= n ; ++ i )
for ( int j = 1; j <= m ; ++ j )
scanf ( "%d" , &w [i] [j] );
int l = 1 , r = 1e9 , ans = 1;
while ( l <= r ) {
mid = ( l + r ) >> 1;
if ( check () ) r = mid - 1 , ans = mid ;
else l = mid + 1;
}
printf ( "%d" , l ) ;
return 0 ;
}