POJ 3281 Dining (Max stream)

POJ 3281 Dining

Question link

N cows, each of which has some favorite foods and drinks, each of which has only one, q: How many cows can match? Every Ox can eat his favorite food and drinks?

Idea: The largest stream, modeling source point to each food connected to an edge, capacity is 1, each beverage linked to a edge capacity is 1, and then because each ox has CAPACITY 1, so we need to split the ox, and then feed it into the ox, and feed the ox out, and run the maximum stream.

Code:

# Include <cstdio> # include <cstring> # include <queue> # include <algorithm> using namespace std; const int MAXNODE = 505; const int MAXEDGE = 100005; typedef int Type; const Type INF = 0x3f3f3f; struct Edge {int u, v; Type cap, flow; Edge () {} Edge (int u, int v, Type cap, Type flow) {this-> u = u; this-> v = v; this-> cap = cap; this-> flow = flow ;}}; struct Dinic {int n, m, s, t; Edge edges [MAXEDGE]; int first [MAXNODE ]; Int next [MAXEDGE]; bool vis [MAXNODE]; Type d [MAXNODE]; int cur [MAXNODE]; vector <int> cut; void init (int n) {this-> n = n; memset (first,-1, sizeof (first); m = 0;} void add_Edge (int u, int v, Type cap) {edges [m] = Edge (u, v, cap, 0); next [m] = first [u]; first [u] = m ++; edges [m] = Edge (v, u, 0, 0); next [m] = first [v]; first [v] = m ++;} bool bfs () {memset (vis, false, sizeof (vis); queue <int> Q; Q. push (s); d [s] = 0; v Is [s] = true; while (! Q. empty () {int u = Q. front (); Q. pop (); for (int I = first [u]; I! =-1; I = next [I]) {Edge & e = edges [I]; if (! Vis [e. v] & e. cap> e. flow) {vis [e. v] = true; d [e. v] = d [u] + 1; Q. push (e. v) ;}}return vis [t];} Type dfs (int u, Type a) {if (u = t | a = 0) return; type flow = 0, f; for (int & I = cur [u]; I! =-1; I = next [I]) {Edge & e = edges [I]; if (d [u] + 1 = d [e. v] & (f = dfs (e. v, min (a, e. cap-e. flow)> 0) {e. flow + = f; edges [I ^ 1]. flow-= f; flow + = f; a-= f; if (a = 0) break;} return flow;} Type Maxflow (int s, int t) {this-> s = s; this-> t = t; Type flow = 0; while (bfs () {for (int I = 0; I <n; I ++) cur [I] = first [I]; flow + = dfs (s, INF);} return flow;} void MinCut () {cut. clear (); for (int I = 0; I < M; I + = 2) {if (vis [edges [I]. u] &! Vis [edges [I]. v]) cut. push_back (I) ;}} gao; int f, d, n; int main () {while (~ Scanf ("% d", & n, & f, & d) {int s = 0, t = f + d + n * 2 + 1; gao. init (t + 1); for (int I = 1; I <= f; I ++) gao. add_Edge (s, I, 1); for (int I = 1; I <= d; I ++) gao. add_Edge (f + I, t, 1); for (int I = 1; I <= n; I ++) {gao. add_Edge (I + f + d, n + f + d + I, 1); int fn, dn; scanf ("% d", & fn, & dn ); int v; while (fn --) {scanf ("% d", & v); gao. add_Edge (v, I + f + d, 1) ;}while (dn --) {scanf ("% d", & v); gao. add_Edge (n + f + d + I, f + v, 1) ;}} printf ("% d \ n", gao. maxflow (s, t);} return 0 ;}

POJ 3281 Dining (Max stream)