[洛谷P4779]【模板】单源最短路径（标准版）

题目大意：单元最短路径（卡$SPFA$）

题解：$dijkstra$($\underline{\hspace{0.5em}}\underline{\hspace{0.5em}}gnu\underline{\hspace{0.5em}}pb\underline{\hspace{0.5em}}ds::priority\underline{\hspace{0.5em}}queue$优化)

卡点：无

C++ Code：

#include <cstdio>
#include <ext/pb_ds/priority_queue.hpp>
#define maxn 100010
#define maxm 200010
using namespace std;
const int inf = 0x3f3f3f3f;
int n, m, S;
int dis[maxn];
int head[maxn], cnt;
struct Edge {
	int to, nxt, w;
} e[maxm];
void add(int a, int b, int c) {
	e[++cnt] = (Edge) {b, head[a], c}; head[a] = cnt;
}
struct cmp {
	inline bool operator () (const int &a, const int &b) const {
		return dis[a] > dis[b];
	}
};
__gnu_pbds::priority_queue<int, cmp> q;
__gnu_pbds::priority_queue<int, cmp>::point_iterator iter[maxn];
void dijkstra(int S) {
	for (int i = 1; i <= n; i++) dis[i] = inf, iter[i] = q.push(i);
	dis[S] = 0;
	q.modify(iter[S], S);
	while (!q.empty()) {
		int u = q.top(); q.pop();
		for (int i = head[u]; i; i = e[i].nxt) {
			int v = e[i].to;
			if (dis[v] > dis[u] + e[i].w) {
				dis[v] = dis[u] + e[i].w;
				q.modify(iter[v], v);
			}
		}
	}
}
int main() {
	scanf("%d%d%d", &n, &m, &S);
	for (int i = 0; i < m; i++) {
		int a, b, c;
		scanf("%d%d%d", &a, &b, &c);
		add(a, b, c);
	}
	dijkstra(S);
	for (int i = 1; i <= n; i++) {
		printf("%d ", dis[i] == inf ? -1 : dis[i]);
	}
	puts("");
	return 0;
}