# CFR 237 E. Build String ( MCMF )

Problem - 237E - Codeforces

1 ≤ N ≤ 100
0 ≤ A[ i ] ≤ 100

MCMF 隨便流。

O( N ** 2 )

```#include <bits/stdc++.h>
using namespace std;

template< class TF, class TC >
struct CostFlow {
static const int MAXV = 10000;
static constexpr TC INF = 1e9;
struct Edge {
int v, r;
TF f;
TC c;
Edge( int _v, int _r, TF _f, TC _c ): v( _v ), r( _r ), f( _f ), c( _c ) {}
};
int n, s, t, pre[ MAXV ], pre_E[ MAXV ], inq[ MAXV ];
TF fl;
TC dis[ MAXV ], cost;
vector< Edge > E[ MAXV ];
CostFlow( int _n, int _s, int _t ): n( _n ), s( _s ), t( _t ), fl( 0 ), cost( 0 ) {}
void add_edge( int u, int v, TF f, TC c ) {
E[ u ].emplace_back( v, E[ v ].size(), f, c );
E[ v ].emplace_back( u, E[ u ].size() - 1, 0, -c );
}
pair< TF, TC > flow() {
while( true ) {
for( int i = 0; i < n; ++i ) {
dis[ i ] = INF;
inq[ i ] = 0;
}
dis[ s ] = 0;
queue< int > que;
que.emplace( s );
while( not que.empty() ) {
int u = que.front();
que.pop();
inq[ u ] = 0;
for( int i = 0; i < E[ u ].size(); ++i ) {
int v = E[ u ][ i ].v;
TC w = E[ u ][ i ].c;
if( E[ u ][ i ].f > 0 and dis[ v ] > dis[ u ] + w ) {
pre[ v ] = u;
pre_E[ v ] = i;
dis[ v ] = dis[ u ] + w;
if( not inq[ v ] ) {
inq[ v ] = 1;
que.emplace( v );
}
}
}
}
if( dis[ t ] == INF ) break;
TF tf = INF;
for( int v = t, u, l; v != s; v = u ) {
u = pre[ v ];
l = pre_E[ v ];
tf = min( tf, E[ u ][ l ].f );
}
for( int v = t, u, l; v != s; v = u ) {
u = pre[ v ];
l = pre_E[ v ];
E[ u ][ l ].f -= tf;
E[ v ][ E[ u ][ l ].r ].f += tf;
}
cost += tf * dis[ t ];
fl += tf;
}
return { fl, cost };
}
};

const int MAXN = 100;

string T;
int N;
string word[ MAXN ];
int limit[ MAXN ];

signed main() {
ios::sync_with_stdio( 0 );
cin >> T;
cin >> N;
for( int i = 0; i < N; ++i ) {
cin>> word[ i ] >> limit[ i ];
}
CostFlow< int, int > mcmf( N + 26 + 2, N + 26, N + 26 + 1 );
for( int i = 0; i < N; ++i ) {
mcmf.add_edge( N + 26, i, limit[ i ], 0 );
vector< int > cnt( 26 );
for( int j = 0; j < word[ i ].size(); ++j ) {
++cnt[ word[ i ][ j ] - 'a' ];
}
for( int j = 0; j < 26; ++j ) if( cnt[ j ] ) {
mcmf.add_edge( i, N + j, cnt[ j ], i + 1 );
}
}
vector< int > T_cnt( 26 );
for( int i = 0; i < T.size(); ++i ) {
++T_cnt[ T[ i ] - 'a' ];
}
for( int i = 0; i < 26; ++i ) if( T_cnt[ i ] ) {
mcmf.add_edge( N + i, N + 26 + 1, T_cnt[ i ], 0 );
}
int flow, cost;
tie( flow, cost ) = mcmf.flow();
if( flow == T.size() ) cout << cost << endl;
else cout << -1 << endl;
return 0;
}
```