hdu_4289

跟3491基本上一样，最小割,不同的是该题,原点和会点都可以设置边

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#define MAXV    402
#define MAXE    80001
#define INF        0x7fffffff
using namespace std;

struct Edge{
    int v, val, next;
}edge[MAXE];

int e_cnt;
int head[MAXV], cur[MAXV], pre[MAXV], dis[MAXV], gap[MAXV];

void insert_arc(int u, int v, int w)
{
    edge[e_cnt].v = v; edge[e_cnt].val = w;
    edge[e_cnt].next = head[u];    head[u] = e_cnt ++;
    swap(u, v);
    edge[e_cnt].v = v; edge[e_cnt].val = 0;
    edge[e_cnt].next = head[u];    head[u] = e_cnt ++;
}

void bfs(int des)
{
    int u, v;
    queue<int> q;
    memset(gap, 0, sizeof(gap));
    memset(dis, -1, sizeof(dis));
    dis[des] = 0;    gap[0] = 1;
    q.push(des);
    while( !q.empty() ) {
        u = q.front(); q.pop();
        for(int i = head[u]; i != -1; i = edge[i].next) {
            v = edge[i].v;
            if( edge[i].val || dis[v] != -1 )     continue;
            dis[v] = dis[u]+1;    q.push(v);    gap[dis[v]] ++;
        }
    }
}

int i_sap(int src, int des, int VN)
{
    int u(src), v, min_dis, max_flow(0), path_flow(INF);
    bfs(src);    pre[u] = u;
    for(int i = 0; i <= VN; i ++)
        cur[i] = head[i];
    while( dis[src] < VN ) {
loop:
        for(int &i = cur[u]; i != -1; i = edge[i].next) {
            v = edge[i].v;
            if( !edge[i].val || dis[u] != dis[v]+1 )    continue;
            pre[v] = u;    path_flow = min(path_flow, edge[i].val);
            u = v;
            if( v == des ) {
                for(u = pre[u]; v != src; v = u, u = pre[u]) {
                    edge[cur[u]].val -= path_flow;    edge[cur[u]^1].val += path_flow;
                }
                max_flow += path_flow; path_flow = INF;
            }
            goto loop;
        }
        min_dis = VN;
        for(int i = head[u]; i != -1; i = edge[i].next) {
            v = edge[i].v;
            if( edge[i].val && min_dis > dis[v] ) {
                cur[u] = i; min_dis = dis[v];
            }
        }
        gap[dis[u]] --;
        if( !gap[dis[u]] )    break;
        dis[u] = min_dis+1;
        gap[dis[u]] ++; u = pre[u];
    }
    return max_flow;
}

int main(int argc, char const *argv[])
{
    //freopen("test.in", "r", stdin);
    int vertex, arc, src, des, v, f, t, ss, ee;
    while( ~scanf("%d %d %d %d", &vertex, &arc, &src, &des) ) {
        e_cnt = 0;    memset(head, -1, sizeof(head));
        ss = 0;    ee = 2*vertex+1;
        insert_arc(ss, src, INF);    insert_arc(des+vertex, ee, INF);

        for(int i = 1; i <= vertex; i ++) {
            scanf("%d", &v);
            insert_arc(i, i+vertex, v);    //insert_arc(i+vertex, i, ve_val[i]);
        }

        for(int i = 0; i < arc; i ++) {
            scanf("%d %d", &f, &t);
            insert_arc(f+vertex, t, INF);
            insert_arc(t+vertex, f, INF);
        }

        printf("%d\n", i_sap(ss, ee, ee));
    }
    return 0;
}