POJ 2987 Firing （最大权闭合子图Dinic)

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题意：公司打算裁员，裁掉某些员工可以获得正收益，而裁掉某些员工会遭受损失。并且员工之间往往存在一定的关系，当某个员工被裁掉之后，在他的关系之下的所有员工都必须被裁掉。现在要求如何裁员才能获得最大收益。
题解：s->正权， 负权->t。  ans = 正权和 - maxflow, 或者 ans = 正权和 - 没有被裁的正权和 - abs(被裁的负权和） （ 正边权进入最小割表示该人没被炒，非正边权进入最小割表示该人被炒）。至于边权放大什么的就不是很理解了····

#include <algorithm>
#include <iostream>
using namespace std;#define MAX 40000
#define INF 99999999999999999
#define min(a,b) (a<b?a:b)struct Edge
{int st, ed;int next;__int64 flow;
} edge[MAX*10];int head[MAX], out[MAX];
int stk[MAX], que[MAX];
int leve[MAX];
bool vis[MAX];
int E, src, sink;void add_edge ( int u, int v, __int64 flw )
{edge[E].st = u;edge[E].ed = v;edge[E].flow = flw;edge[E].next = head[u];head[u] = E++;edge[E].st = v;edge[E].ed = u;edge[E].flow = 0;edge[E].next = head[v];head[v] = E++;
}bool dinic_bfs()
{memset(leve,-1,sizeof(leve));int front, rear, u, v, i;front = rear = 0;que[rear++] = src;leve[src] = 0;while ( front != rear ){u = que[front];front = ( front + 1 ) % MAX;for ( i = head[u]; i != -1; i = edge[i].next ){v = edge[i].ed;if ( edge[i].flow > 0 && leve[v] == -1 ){leve[v] = leve[u] + 1;que[rear] = v;rear = ( rear + 1 ) % MAX;}}}return leve[sink] != -1;
}__int64 Dinic ()
{__int64 maxFlow = 0;while ( dinic_bfs() ){int top = 0, u = src, i;for ( i = src; i <= sink; i++ ) out[i] = head[i];while ( out[src] != -1 ){if ( u == sink ){__int64 dd = INF;for ( i = top - 1; i >= 0; i-- )dd = min ( edge[stk[i]].flow, dd );for ( i = top - 1; i >= 0; i-- ){edge[stk[i]].flow -= dd;edge[stk[i]^1].flow += dd;if ( edge[stk[i]].flow == 0 ) top = i;}maxFlow += dd;u = edge[stk[top]].st;}else if ( out[u] != -1 && edge[out[u]].flow > 0 && leve[u] + 1 == leve[edge[out[u]].ed] ){stk[top++] = out[u];u = edge[out[u]].ed;}else{while ( top > 0 && u != src && out[u] == -1 )u = edge[stk[--top]].st;out[u] = edge[out[u]].next;}}}return maxFlow;
}int dfs ( int u )
{vis[u] = true;int cnt = 1;for ( int i = head[u]; i != -1; i = edge[i].next )if ( ! vis[edge[i].ed] && edge[i].flow > 0 )cnt += dfs(edge[i].ed);return cnt;
}int main()
{__int64 sum = 0;int n, m, u, v, b;scanf("%d%d",&n,&m);E = src = 0;sink = n + 1;memset(head,-1,sizeof(head));for ( int i = 1; i <= n; i++ ){scanf("%d",&b);if ( b > 0 ){sum += b;add_edge ( src, i, b );}else add_edge ( i, sink, -b );}while ( m-- ){scanf("%d%d",&u,&v);add_edge ( u, v, INF );}memset(vis,0,sizeof(vis));__int64 maxFlow = Dinic();int cnt = dfs ( src );printf("%d %I64d\n", cnt - 1, sum - maxFlow );return 0;
}

#include <algorithm>
#include <iostream>
using namespace std;#define MAX 60000
#define INF 9999999999999
#define min(a,b) ((a)<(b)?(a):(b))struct Edge
{int st, ed;int flow;int next;
} edge[MAX*3];int head[MAX], out[MAX];
int stk[MAX], que[MAX];
int leve[MAX], vis[MAX];
int E, src, sink;void add_edge ( int u, int v, __int64 flw )
{edge[E].st = u;edge[E].ed = v;edge[E].flow = flw;edge[E].next = head[u];head[u] = E++;edge[E].st = v;edge[E].ed = u;edge[E].flow = 0;edge[E].next = head[v];head[v] = E++;
}__int64 Dinic()
{__int64 maxFlow = 0;int front, rear, top;int cur, u, i;while ( 1 ){for ( i = src; i <= sink; i++ ) leve[i] = -1;front = rear = leve[src] = 0;que[rear++] = src;while ( front != rear ){u = que[front];front = ( front + 1 ) % MAX;for ( i = head[u]; i != -1; i = edge[i].next){if ( edge[i].flow > 0 && leve[edge[i].ed] == -1 ){leve[edge[i].ed] = leve[u] + 1;que[rear]= edge[i].ed;rear = ( rear + 1 ) % MAX;}}}if ( leve[sink] == -1 ) break;for ( i = src; i <= sink; i++ ) out[i] = head[i];top = 0;while ( 1 ){if ( top == 0 ){for ( cur = out[src]; cur != -1; cur = edge[cur].next )if ( edge[cur].flow > 0 && out[edge[cur].ed] != -1 && leve[edge[cur].ed] == 1 )break;if ( cur < 0 ) break;stk[top++] = cur;out[src] = edge[cur].next;}u = edge[stk[top-1]].ed;if ( u == sink ){__int64 dd = INF, index = -1;for ( i = top - 1; i >= 0; i-- ){if ( dd >= edge[stk[i]].flow ){dd = edge[stk[i]].flow;index = i;}}maxFlow += dd;for ( i = 0; i < top; i++ ){edge[stk[i]].flow -= dd;edge[stk[i]^1].flow += dd;    }top = index;}else{for( cur = out[u]; cur != -1; cur = edge[cur].next )if ( edge[cur].flow && out[edge[cur].ed] != -1 && leve[u] + 1 == leve[edge[cur].ed] )break;if ( cur != -1 ){stk[top++] = cur;out[u] = edge[cur].next;}else{out[u] = -1;top--;}}}}return maxFlow;
}int dfs ( int u )
{vis[u] = true;int v, i, cnt = 1;for ( i = head[u]; i != -1; i = edge[i].next ){v = edge[i].ed;if ( ! vis[v] && edge[i].flow > 0 )cnt += dfs(v);}return cnt;
}int main()
{__int64 sum = 0;int n, m, u, v, b;scanf("%d%d",&n,&m);E = src = 0;sink = n + 1;memset(head,-1,sizeof(head));for ( int i = 1; i <= n; i++ ){scanf("%d",&b);if ( b > 0 ){sum += b;add_edge ( src, i, b );}else add_edge ( i, sink, -b );}while ( m-- ){scanf("%d%d",&u,&v);add_edge ( u, v, INF );}memset(vis,0,sizeof(vis));__int64 maxFlow = Dinic();int cnt = dfs ( src ) - 1;printf("%d %I64d\n", cnt, sum - maxFlow);return 0;
}

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