这两天学习了最大流,下面是ISAP算法模板:
const int inf = 0x3fffffff; template <int N, int M> struct Isap { int top; int d[N], pre[N], cur[N], gap[N]; struct Vertex{ int head; } V[N]; struct Edge{ int v, next; int c, f; } E[M]; void init(){ memset(V, -1, sizeof(V)); top = 0; } void add_edge(int u, int v, int c){ E[top].v = v; E[top].c = c; E[top].f = 0; E[top].next = V[u].head; V[u].head = top++; } void add(int u,int v, int c){ add_edge(u, v, c); add_edge(v, u, 0); } void set_d(int t){ queue<int> Q; memset(d, -1, sizeof(d)); memset(gap, 0, sizeof(gap)); d[t] = 0; Q.push(t); while(!Q.empty()) { int v = Q.front(); Q.pop(); ++gap[d[v]]; for(int i = V[v].head; ~i; i = E[i].next) { int u = E[i].v; if(d[u] == -1) { d[u] = d[v] + 1; Q.push(u); } } } } int sap(int s, int t, int num) { set_d(t); int ans = 0, u = s; int flow = inf; memcpy(cur, V, sizeof(V)); while(d[s] < num) { int &i = cur[u]; for(; ~i; i = E[i].next) { int v = E[i].v; if(E[i].c > E[i].f && d[u] == d[v] + 1) { u = v; pre[v] = i; flow = min(flow, E[i].c - E[i].f); if(u == t) { while(u != s) { int j = pre[u]; E[j].f += flow; E[j^1].f -= flow; u = E[j^1].v; } ans += flow; flow = inf; } break; } } if(i == -1) { if(--gap[d[u]] == 0) break; int dmin = num - 1; cur[u] = V[u].head; for(int j = V[u].head; ~j; j = E[j].next) if(E[j].c > E[j].f) dmin = min(dmin, d[E[j].v]); d[u] = dmin + 1; ++gap[d[u]]; if(u != s) u = E[pre[u] ^ 1].v; } } return ans; } }; Isap<1000, 1000000> Sap; 调用方式: Sap.init(); //建边前调用 Sap.add(u, v, c); //在u->v之间建一条容量为c的边 Sap.sap(s, t, num); //s为源点,t为汇点,num为边的数量
原文地址:http://blog.csdn.net/lyhvoyage/article/details/26588189