POJ 1149 PIGS ( 网络流 )

主要是建图有些小烦，若几个节点流量的来源或者去向完全相同，且流量为 INF，将它们合并成一个节点。

若从两点间有且仅有一条容量为 INF 的边，将两点合并成一个节点。

#include <iostream>
#include <cstring>
#include <queue>
using namespace std;

const int INF = 0x7fffffff;
const int MAXN = 110;

int capacity[MAXN][MAXN], flow[MAXN][MAXN];
int parent[MAXN], residual[MAXN];
int max_flow, node_num;

void edmond_karp( int source, int target ) {

queue< int > Q;
memset( flow, 0, sizeof( flow ) );
memset( parent, 0, sizeof( parent ) );
max_flow = 0;

while ( true ) {
memset( residual, 0, sizeof( residual ) );
residual[source] = INF;
Q.push( source );
while ( !Q.empty() ) {
int u = Q.front();
Q.pop();
for( int v = 0; v <= node_num + 1; ++v ) {
if( !residual[v] && capacity[u][v] > flow[u][v] ) {
parent[v] = u;
Q.push( v );
residual[v] = residual[u] < capacity[u][v] - flow[u][v] ? residual[u] : capacity[u][v] - flow[u][v];
}
}
}

if( residual[target] == 0 )
break;

for( int u = target; u != source; u = parent[u] ) {
flow[parent[u]][u] += residual[target];
flow[u][parent[u]] -= residual[target];
}

max_flow += residual[target];

}

}

int main() {

int pighouses_num, customers_num;
int pighouses_capacity[1010];
int visited_by_somebody[1010];

while( cin >> pighouses_num >> customers_num ) {
memset( capacity, 0, sizeof( capacity ) );
memset( visited_by_somebody, 0, sizeof( visited_by_somebody ) );
int source = 0, target = customers_num + 1;
node_num = customers_num;

for( int i = 1; i <= pighouses_num; ++i )
cin >> pighouses_capacity[i];

for( int i = 1; i <= customers_num; ++i ) {

int keys_num;
cin >> keys_num;

for( int j = 0; j < keys_num; ++j ) {

int temp;
cin >> temp;

if( visited_by_somebody[temp] == 0 )
capacity[source][i] += pighouses_capacity[temp];
else
capacity[visited_by_somebody[temp]][i] = INF;
visited_by_somebody[temp] = i;

}

cin >> capacity[i][target];

}

edmond_karp( source, target );
cout << max_flow << endl;

}

return 0;

}