为什么SPFA不让过

这就是故意卡我SPFA的吗？？？ lgcmzz

#include<bits/stdc++.h>
using namespace std;
const int N = 2e5 + 5;
int n, m, s, idx, e[N], ne[N], w[N], h[N], dist[N];
bool st[N];
void add(int a, int b, int c) {
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx++;
}
int spfa() {
    memset(dist, 0x3f, sizeof dist);
    dist[s] = 0;
    queue<int> q;
    q.push(s);
    st[s] = true;
    while(q.size()) {
        int t = q.front();
        q.pop();
        st[t] = false;
        for(int i = h[t]; i != -1; i = ne[i]) {
            int j = e[i];
            if(dist[j] > dist[t] + w[i]) {
                dist[j] = dist[t] + w[i];
                if(!st[j]) {
                    q.push(j);
                    st[j] = true;
                }
            }
        }
    }
    if(dist[n] == 0x3f3f3f3f) return -1000000000;
    return dist[n];
}
int main () {
    scanf("%d%d%d", &n, &m, &s);
    memset(h, -1, sizeof h);
    int a, b, c;
    for(int i = 1;i <= m;++i) scanf("%d%d%d", &a, &b, &c), add(a, b, c);
    int t = spfa();
    if(t == -1000000000) printf("impossible"), exit(0);
    for(int i = 1;i <= n;++i) printf("%d ", dist[i]);
    return 0;
}