题目链接：https://www.luogu.org/problemnew/show/P3381
把bfs变成spfa
1 #include <queue> 2 #include <cstdio> 3 #include <cstring> 4 #include <iostream> 5 #include <algorithm> 6 using namespace std; 7 const int maxn = 1000000 + 10; 8 int n, m, s, t, maxflow, mincost, dis[maxn], flow[maxn], pre[maxn], last[maxn]; 9 struct edge{ 10 int to, next, cost, flow; 11 }e[maxn<<2]; 12 int head[maxn], cnt = -1; 13 bool vis[maxn]; 14 queue<int> q; 15 void add(int u, int v, int w, int c) 16 { 17 e[++cnt].next = head[u]; 18 e[cnt].to = v; 19 e[cnt].cost = c; 20 e[cnt].flow = w; 21 head[u] = cnt; 22 23 e[++cnt].next = head[v]; 24 e[cnt].to = u; 25 e[cnt].cost = -c; 26 e[cnt].flow = 0; 27 head[v] = cnt; 28 } 29 bool SPFA(int s, int t) 30 { 31 memset(dis, 0x7f, sizeof(dis)); 32 memset(flow, 0x7f, sizeof(flow)); 33 memset(vis, 0, sizeof(vis)); 34 q.push(s); pre[t] = -1; vis[s] = 1; dis[s] = 0; 35 while(!q.empty()) 36 { 37 int now = q.front(); q.pop(); 38 vis[now] = 0; 39 for(int i = head[now]; i != -1; i = e[i].next) 40 { 41 if(e[i].flow > 0 && dis[e[i].to] > dis[now] + e[i].cost) 42 { 43 dis[e[i].to] = dis[now] + e[i].cost; 44 pre[e[i].to] = now; 45 last[e[i].to] = i; 46 flow[e[i].to] = min(flow[now], e[i].flow); 47 if(!vis[e[i].to]) 48 { 49 q.push(e[i].to); 50 vis[e[i].to] = 1; 51 } 52 } 53 } 54 } 55 return pre[t] != -1; 56 } 57 void MCMF(int s, int t) 58 { 59 while(SPFA(s, t)) 60 { 61 int now = t; 62 maxflow += flow[t]; 63 mincost += flow[t] * dis[t]; 64 while(now != s) 65 { 66 e[last[now]].flow -= flow[t]; 67 e[last[now]^1].flow += flow[t]; 68 now = pre[now]; 69 } 70 } 71 } 72 int main() 73 { 74 memset(head, -1, sizeof(head)); 75 scanf("%d%d%d%d",&n,&m,&s,&t); 76 for(int i = 1; i <= m; i++) 77 { 78 int u, v, w, c; 79 scanf("%d%d%d%d",&u,&v,&w,&c); 80 add(u, v, w, c); 81 } 82 MCMF(s, t); 83 printf("%d %d ",maxflow, mincost); 84 return 0; 85 }
