acwing 851. spfa求最短路

输入样例：
3 3
1 2 5
2 3 -3
1 3 4
输出样例：
2

#include 
#include 
#include 
#include 
#include using namespace std;


/* acwing 851 
3 3
1 2 5
2 3 -3
1 3 4
*/

const int MAX_N = 100010;

vectorint, int>> v[MAX_N];
int dist[MAX_N];
int st[MAX_N];
int n, m;

int solve()
{
    memset(dist, 0x3f, sizeof(dist));
    dist[1] = 0;

    queueint> q;
    q.push(1);
    st[1] = 1;
    
    while (!q.empty()) {
        auto e = q.front();
        q.pop();

        st[e] = false;

        for (int i = 0; i ) {
            int target = v[e][i].first;
            int len = v[e][i].second;
            if (dist[target] > dist[e] + len) {
                dist[target] = dist[e] + len;
                if (!st[target]) {
                    //队列中不存在target节点 插入队列
                    q.push(target);
                    st[target] = 1;
                }
            }
        }
    }

    if (dist[n] == 0x3f3f3f3f) return -1;
    return dist[n];
}


int main()
{
    //cin >> n >> m;
    scanf("%d%d",&n,&m);
    //v.resize(n+1);

    for (int i = 0; i ) {
        int a, b, c;
        //cin >> a >> b >> c;
        scanf("%d%d%d",&a,&b,&c);
        v[a].push_back({ b,c });
    }

    int ret = solve();

    if (ret == -1) printf("impossible\n"); 
    else printf("%d\n",dist[n]);

    return 0;
}