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 0x7fffffffusing 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;}
