add shortest path faster algorithm

Author: AmazingCaddy

template/Graph/SPFA.cpp

@@ -0,0 +1,100 @@
+// Shortest Path Faster Algorithm
+#include <iostream>
+#include <queue>
+using namespace std;
+
+const int maxn = 1005;
+const int maxm = 20005;
+const int inf = 0x3f3f3f3f;
+
+struct edge{
+	int v, w;
+	int next;
+};
+
+int total;
+int head[maxn];
+edge e[maxm];
+
+int dis[maxn];
+int inqueue[maxn];
+int cnt[maxn];
+
+void init(int n) {
+	total = 0;
+	for (int i = 0; i < n; i ++) {
+		head [i] = -1;
+	}
+}
+
+void addedge(int u, int v, int w) {
+	e[total].v = v;
+	e[total].w = w;
+	e[total].next = head[u];
+	head[u] = total;
+	total ++;
+}
+
+int spfa (int n, int s, int t = -1) {
+	for (int i = 0; i < n; i ++) {
+		dis[i] = inf;
+		inqueue[i] = 0;
+		cnt[i] = 0;
+	}
+	queue<int> que;
+	que.push(s);
+	inqueue[s] = 1;
+	cnt[s] = 1;
+	dis[s] = 0;
+	while (!que.empty()) {
+		int u = que.front();
+		que.pop();
+		inqueue[u] = 0;
+		for (int i = head[u]; i != -1; i = e[i].next) {
+			int v = e[i].v;
+			if (dis[u] + e[i].w < dis[v]) {
+				dis[v] = dis[u] + e[i].w;
+				if (!inqueue[v]) {
+					que.push(v);
+					inqueue[v] = 1;
+					cnt[v] ++;
+					if (cnt[v] > n) {
+						return -1;
+					}
+				}
+			}
+		}
+	}
+	if (t == -1) {
+		t = n - 1;
+	}
+	return dis[t];
+}
+
+int main(int argc, char const *argv[]) {
+	int n, m, s, t;
+	int u, v, w;
+	int des;
+	while (scanf ("%d%d%d", &n, &m, &s) == 3) {
+		init(n);
+		s --;
+		for (int i = 0; i < m; i ++) {
+			scanf ("%d%d%d", &u, &v, &w);
+			u --;
+			v --;
+			addedge(v, u, w);
+		}
+		spfa(n, s);
+		scanf ("%d", &t);
+		int ans = inf;
+		for (int i = 0; i < t; i ++) {
+			scanf ("%d", &des);
+			ans = min(ans, dis[des - 1]);
+		}
+		if (ans == inf) {
+			ans = -1;
+		}
+		cout << ans << "\n";
+	}
+	return 0;
+}