队列优化的Bellman-Ford算法（SPFA算法）

Author: Dev-XYS

Bellman-Ford(Queue-Optimised).cpp

@@ -0,0 +1,95 @@
+#include <cstdio>
+
+#define INF 1000000000
+
+using namespace std;
+
+struct vertex
+{
+	int first_edge;
+	int dis;
+}V[100010];
+
+struct edge
+{
+	int endp, next;
+	int w;
+}E[1000010];
+
+int ec = 1;
+int ivc, iec;
+
+int Q[200000];
+int hp = 0, tp = 0;
+
+void enqueue(int x)
+{
+	Q[tp] = x;
+	tp++;
+	tp %= 200000;
+}
+
+int dequeue()
+{
+	int ret = Q[hp];
+	hp++;
+	hp %= 200000;
+	return ret;
+}
+
+bool empty()
+{
+	return hp == tp;
+}
+
+void add_edge(int u, int v, int w)
+{
+	E[ec].next = V[u].first_edge;
+	V[u].first_edge = ec;
+	E[ec].endp = v;
+	E[ec].w = w;
+	ec++;
+}
+
+void initial_single_source(int s)
+{
+	for (int i = 1; i <= ivc; i++)
+	{
+		V[i].dis = INF;
+	}
+	V[s].dis = 0;
+}
+
+void SPFA(int s)
+{
+	initial_single_source(s);
+	enqueue(s);
+	while (!empty())
+	{
+		int u = dequeue();
+		for (int cur = V[u].first_edge; cur != 0; cur = E[cur].next)
+		{
+			int newdis = V[u].dis + E[cur].w;
+			if (newdis < V[E[cur].endp].dis)
+			{
+				V[E[cur].endp].dis = newdis;
+				enqueue(E[cur].endp);
+			}
+		}
+	}
+}
+
+int main()
+{
+	scanf("%d%d", &ivc, &iec);
+	for (int i = 0; i < iec; i++)
+	{
+		int u, v, w;
+		scanf("%d%d%d", &u, &v, &w);
+		add_edge(u, v, w);
+		add_edge(v, u, w);
+	}
+	SPFA(1);
+	printf("%d", V[ivc].dis);
+	return 0;
+}