最大流Edmonds-Karp算法（附CodeVS - 1993草地排水代码）

Edmonds-Karp.cpp

@@ -0,0 +1,136 @@
+#include <cstdio>
+#include <cstring>
+
+#define VERTEX_COUNT 210
+#define EDGE_COUNT 20000
+
+using namespace std;
+
+struct vertex
+{
+	int first_edge;
+	int pree, prev;
+}V[VERTEX_COUNT];
+
+bool vis[VERTEX_COUNT];
+
+struct edge
+{
+	int endp, next;
+	int flow;
+}E[EDGE_COUNT];
+
+int ec = 2;
+int ivc, iec;
+
+int maxflow = 0;
+
+int Q[VERTEX_COUNT];
+int hp = 0, tp = 0;
+
+inline int min(int x, int y)
+{
+	return x < y ? x : y;
+}
+
+void add_edge(int u, int v, int f)
+{
+	E[ec].next = V[u].first_edge;
+	V[u].first_edge = ec;
+	E[ec].endp = v;
+	E[ec].flow = f;
+	ec++;
+}
+
+inline void enqueue(int x)
+{
+	Q[tp++] = x;
+}
+
+inline int dequeue()
+{
+	return Q[hp++];
+}
+
+inline bool isempty()
+{
+	return hp == tp;
+}
+
+inline void empty()
+{
+	hp = tp = 0;
+}
+
+void Edmonds_Karp(int s, int t)
+{
+	bool has_ap;
+
+	do
+	{
+		has_ap = false;
+		memset(vis, false, sizeof(vis));
+		empty();
+		enqueue(s);
+		while (!isempty())
+		{
+			int u = dequeue();
+			for (int cur = V[u].first_edge; cur != 0; cur = E[cur].next)
+			{
+				if (E[cur].flow > 0)
+				{
+					if (E[cur].endp == t)
+					{
+						has_ap = true;
+						int p = u, pathmin = E[cur].flow;
+						while (p != 1)
+						{
+							pathmin = min(pathmin, E[V[p].pree].flow);
+							p = V[p].prev;
+						}
+						p = u;
+						E[cur].flow -= pathmin;
+						E[cur ^ 1].flow += pathmin;
+						while (p != 1)
+						{
+							E[V[p].pree].flow -= pathmin;
+							E[V[p].pree ^ 1].flow += pathmin;
+							p = V[p].prev;
+						}
+						maxflow += pathmin;
+						goto END;
+					}
+					else if (vis[E[cur].endp] == false)
+					{
+						V[E[cur].endp].pree = cur;
+						V[E[cur].endp].prev = u;
+						vis[E[cur].endp] = true;
+						enqueue(E[cur].endp);
+					}
+				}
+			}
+		}
+
+		END:;
+	} while (has_ap == true);
+}
+
+int main()
+{
+	// e.g. CodeVS - 1993.
+
+	scanf("%d%d", &iec, &ivc);
+	for (int i = 0; i < iec; i++)
+	{
+		int u, v, f;
+		scanf("%d%d%d", &u, &v, &f);
+		add_edge(u, v, f);
+		add_edge(v, u, 0);
+	}
+
+	Edmonds_Karp(1, ivc);
+
+	printf("%d", maxflow);
+
+	return 0;
+}