题目链接：https://www.luogu.org/problemnew/show/P3376
1 #include <iostream> 2 #include <cstdio> 3 #include <algorithm> 4 #include <queue> 5 #include <cstring> 6 using namespace std; 7 const int inf = 1e9; 8 const int maxn = 1000010; 9 int n, m, s, t, deep[maxn], maxflow; 10 struct EDG{ 11 int next, to, flow; 12 }edge[maxn]; 13 int cnt = -1, head[maxn], cur[maxn]; 14 queue<int> q; 15 16 void add(int u, int v, int w, bool flag) 17 { 18 edge[++cnt].next = head[u]; 19 edge[cnt].to = v; 20 if(flag) edge[cnt].flow = w; 21 head[u] = cnt; 22 } 23 24 bool bfs(int s, int t) 25 { 26 memset(deep, 0x7f, sizeof(deep)); 27 while(!q.empty()) q.pop(); 28 for(int i = 1; i <= n; i++) cur[i] = head[i]; 29 deep[s] = 0; 30 q.push(s); 31 32 while(!q.empty()) 33 { 34 int now = q.front(); q.pop(); 35 for(int i = head[now]; i != -1; i = edge[i].next) 36 { 37 if(deep[edge[i].to] > inf && edge[i].flow) 38 { 39 deep[edge[i].to] = deep[now]+1; 40 q.push(edge[i].to); 41 } 42 } 43 } 44 if(deep[t] < inf) return true; 45 else return false; 46 } 47 48 int dfs(int now, int t, int limit) 49 { 50 if(!limit || now == t) return limit; 51 int flow = 0, f; 52 for(int i = cur[now]; i != -1; i = edge[i].next) 53 { 54 cur[now] = i; 55 if(deep[edge[i].to] == deep[now]+1 && (f = dfs(edge[i].to, t, min(limit, edge[i].flow)))) 56 { 57 flow += f; 58 limit -= f; 59 edge[i].flow -= f; 60 edge[i^1].flow += f; 61 if(!limit) break; 62 } 63 } 64 return flow; 65 } 66 void Dinic(int s, int t) 67 { 68 while(bfs(s,t)) 69 maxflow += dfs(s,t,inf); 70 } 71 int main() 72 { 73 memset(head, -1, sizeof(head)); 74 scanf("%d%d%d%d",&n,&m,&s,&t); 75 for(int i = 1; i <= m; i++) 76 { 77 int u, v, w; 78 scanf("%d%d%d",&u,&v,&w); 79 add(u,v,w,1); 80 add(v,u,w,0); 81 } 82 Dinic(s,t); 83 printf("%d",maxflow); 84 return 0; 85 }
