题目

#include <bits/stdc++.h>
using namespace std;
int n, m, cnt;

struct edge {
	long long to, cost, nex;
} e[40020];
long long dis[20020];
int head[20020];
bool vis[20020];

void add(int x, int y, int z) {
	e[++cnt].to = y;
	e[cnt].cost = z;
	e[cnt].nex = head[x];
	head[x] = cnt;
}

void spfa() {
	queue<int>Q;
	for (int i = 1; i <= n; i++)
		dis[i] = 123456789;
	dis[1] = 0;
	vis[1] = 1;
	Q.push(1);
	while (!Q.empty()) {
		int u = Q.front();
		Q.pop();
		vis[u] = 0;
		for (int i = head[u]; i; i = e[i].nex) {
			int v = e[i].to;
			if (dis[v] > dis[u] + e[i].cost) {
				dis[v] = dis[u] + e[i].cost;
				if (!vis[v]) {
					vis[v] = 1;
					Q.push(v);
				}
			}
		}
	}
}

int main() {
	cin >> n >> m;
	for (int i = 1; i <= m; i++) {
		int x, y, z;
		cin >> x >> y >> z;
		add(x, y, z);
	}
	spfa();
	cout << dis[n];
}

WA了一个点