LiberOJ ~ 116 ~ 有源匯有上下界最小流 (模板題)
阿新 • • 發佈:2018-12-09
#include<bits/stdc++.h> using namespace std; const int MAXN = 1e5 + 5; const int INF = 0x3f3f3f3f; struct Edge { int from, to, cap, flow; //起點,終點,容量,流量 Edge(int u, int v, int c, int f) : from(u), to(v), cap(c), flow(f) {} }; struct Dinic { int n, m, s, t; //結點數,邊數(包括反向弧),源點s,匯點t vector<Edge> edges; //邊表。edges[e]和edges[e^1]互為反向弧 vector<int> G[MAXN]; //鄰接表,G[i][j]表示結點i的第j條邊在edges陣列中的序號 int d[MAXN]; //從起點到i的距離(層數差) int cur[MAXN]; //當前弧下標 bool vis[MAXN]; //BFS分層使用 void init(int n) { this->n = n; edges.clear(); for (int i = 0; i <= n; i++) G[i].clear(); } void AddEdge(int from, int to, int cap) { edges.push_back(Edge(from, to, cap, 0)); edges.push_back(Edge(to, from, 0, 0)); m = edges.size(); G[from].push_back(m - 2); G[to].push_back(m - 1); } bool BFS()//構造分層網路 { memset(vis, 0, sizeof(vis)); queue<int> Q; d[s] = 0; vis[s] = true; Q.push(s); while (!Q.empty()) { int x = Q.front(); Q.pop(); for (int i = 0; i < G[x].size(); i++) { Edge& e = edges[G[x][i]]; if (!vis[e.to] && e.cap > e.flow) { vis[e.to] = true; d[e.to] = d[x] + 1; Q.push(e.to); } } } return vis[t]; } int DFS(int x, int a)//沿阻塞流增廣 { if (x == t || a == 0) return a; int flow = 0, f; for (int& i = cur[x]; i < G[x].size(); i++)//從上次考慮的弧 { Edge& e = edges[G[x][i]]; if (d[x] + 1 == d[e.to] && (f = DFS(e.to, min(a, e.cap - e.flow))) > 0)//多路增廣 { e.flow += f; edges[G[x][i]^1].flow -= f; flow += f; a -= f; if (a == 0) break; } } return flow; } int MaxFlow(int s, int t) { this->s = s; this->t = t; int flow = 0; while (BFS()) { memset(cur, 0, sizeof(cur)); flow += DFS(s, INF); } return flow; } }solve; const int MAXM = 125003+5; int n, m, s, t, down[MAXM], up, sum[MAXN]; int main() { scanf("%d%d%d%d", &n, &m, &s, &t); int tot = 0; memset(sum, 0, sizeof(sum)); int vs = 0, vt = n+1; solve.init(vt+2); for (int i = 0; i < m; i++) { int u, v; scanf("%d%d%d%d", &u, &v, &down[i], &up); solve.AddEdge(u, v, up-down[i]); sum[u] -= down[i]; sum[v] += down[i]; } for (int i = 0; i <= vt; i++) { if (sum[i] < 0) solve.AddEdge(i, vt, -sum[i]); else solve.AddEdge(vs, i, sum[i]), tot += sum[i]; } int MF = solve.MaxFlow(vs, vt);//先跑一遍最大流,將可以減小的流都減小 solve.AddEdge(t, s, INF); MF += solve.MaxFlow(vs, vt);//再跑一遍最大流 if (MF != tot) printf("please go home to sleep\n"); else { int ans = solve.edges[solve.m-2].flow;//最終t->s邊中的流量就是最小流 printf("%d\n", ans); } return 0; } /* 7 12 6 7 6 1 0 2147483647 1 7 0 2147483647 6 2 0 2147483647 2 7 0 2147483647 6 3 0 2147483647 3 7 0 2147483647 6 4 0 2147483647 4 7 0 2147483647 6 5 0 2147483647 5 7 0 2147483647 5 1 1 2147483647 3 4 1 2147483647 */