#include <iostream>#include <cstring>#include <deque>using namespace std;const int N = 1000010, M = 2000010;const int INF = 0x3f3f3f3f;int n, m, s, t;int h[N], e[M], ne[M], w[M], idx;int dist[N];bool st[N];int cnt[N];deque<int> q;void add(int a, int b, int c) { e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx ++;}bool spfa() { memset(dist, 0x3f, sizeof dist); dist[s] = 0; q.push_back(s); st[s] = true; while (!q.empty()) { int t = q.front(); q.pop_front(); st[t] = false; for (int i = h[t]; ~i; i = ne[i]) { int j = e[i]; if (dist[j] > dist[t] + w[i]) { dist[j] = dist[t] + w[i]; cnt[j] = cnt[t] + 1; if (cnt[j] >= n) return false; if (!st[j]) { if (!q.empty() && dist[j] < dist[q.front()]) q.push_front(j); else q.push_back(j); st[j] = true; } } } } return true;}int main() { scanf("%d%d%d%d", &n, &m, &s, &t); memset(h, -1, sizeof h); while (m --) { int a, b, c; scanf("%d%d%d", &a, &b, &c); add(a, b, c); add(b, a, c); } if (spfa()) cout << dist[t] << endl; else puts("无解"); return 0;}在不用STL容器的前提下实现这个代码

好的，以下是不使用STL容器的实现：

#include <iostream>
#include <cstring>

using namespace std;

const int N = 1000010, M = 2000010;
const int INF = 0x3f3f3f3f;

int n, m, s, t;
int h[N], e[M], ne[M], w[M], idx;
int dist[N];
bool st[N];
int cnt[N];
int q[N];

void add(int a, int b, int c)
{
    e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx ++;
}

bool spfa()
{
    memset(dist, 0x3f, sizeof dist);
    dist[s] = 0;
    int hh = 0, tt = 0;
    q[tt ++] = s;
    st[s] = true;

    while (hh != tt)
    {
        int t = q[hh ++];
        if (hh == N) hh = 0;
        st[t] = false;

        for (int i = h[t]; ~i; i = ne[i])
        {
            int j = e[i];
            if (dist[j] > dist[t] + w[i])
            {
                dist[j] = dist[t] + w[i];
                cnt[j] = cnt[t] + 1;

                if (cnt[j] >= n) return false;

                if (!st[j])
                {
                    q[tt ++] = j;
                    if (tt == N) tt = 0;
                    st[j] = true;
                }
            }
        }
    }

    return true;
}

int main()
{
    scanf("%d%d%d%d", &n, &m, &s, &t);
    memset(h, -1, sizeof h);
    while (m --)
    {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        add(a, b, c);
        add(b, a, c);
    }

    if (spfa()) cout << dist[t] << endl;
    else puts("无解");

    return 0;
}