加入gap优化的ISAP算法（附CodeVS - 1993 草地排水代码）

Improved-Shortest-Augmenting-Path(Gap-Optimised).cpp

@@ -0,0 +1,98 @@
+#include <cstdio>
+
+#define INF 1000000000
+#define VERTEX_COUNT 210
+#define EDGE_COUNT 410
+
+using namespace std;
+
+struct vertex
+{
+	int first, dis;
+}V[VERTEX_COUNT];
+
+struct edge
+{
+	int endp, next, lower, upper, flow;
+}E[EDGE_COUNT];
+
+int ivc, iec, ec = 2, gap[VERTEX_COUNT], src, sink;
+
+inline int min(int x, int y)
+{
+	return x < y ? x : y;
+}
+
+void init()
+{
+	src = 1;
+	sink = ivc;
+	gap[0] = ivc;
+}
+
+void add_edge(int u, int v, int lower, int upper, int flow)
+{
+	E[ec].next = V[u].first;
+	V[u].first = ec;
+	E[ec].endp = v;
+	E[ec].lower = lower;
+	E[ec].upper = upper;
+	E[ec].flow = flow;
+	ec++;
+}
+
+int isap(int u, int curf)
+{
+	if (u == sink)
+	{
+		return curf;
+	}
+	int totalf = 0, mindis = ivc;
+	for (int cur = V[u].first; cur != 0 && totalf < curf; cur = E[cur].next)
+	{
+		if (E[cur].flow > 0)
+		{
+			if (V[u].dis == V[E[cur].endp].dis + 1)
+			{
+				int f = isap(E[cur].endp, min(E[cur].flow, curf - totalf));
+				totalf += f;
+				E[cur].flow -= f;
+				E[cur ^ 1].flow += f;
+			}
+			mindis = min(mindis, V[E[cur].endp].dis);
+		}
+	}
+	if (totalf == 0)
+	{
+		gap[V[u].dis]--;
+		if (gap[V[u].dis] == 0) V[src].dis = ivc;
+		V[u].dis = mindis + 1;
+		gap[V[u].dis]++;
+	}
+	return totalf;
+}
+
+int max_flow()
+{
+	int res = 0;
+	while (V[src].dis < ivc)
+	{
+		res += isap(src, INF);
+	}
+	return res;
+}
+
+int main()
+{
+	int u, v, f;
+	scanf("%d%d", &iec, &ivc);
+	for (int i = 0; i < iec; i++)
+	{
+		scanf("%d%d%d", &u, &v, &f);
+		add_edge(u, v, 0, 0, f);
+		add_edge(v, u, 0, 0, 0);
+	}
+	init();
+	printf("%d", max_flow());
+	return 0;
+}