POJ 2987 Firing （最大权闭合子图Dinic)

来源：互联网发布：mac抹掉磁盘重装系统编辑：程序博客网时间：2024/05/22 18:22

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;}