MulMatrix - shortest path after right k edges (what the fuck is this)

#include <bits/stdc++.h>
#define TASK "CROBOT"
using namespace std;
const long long oo = 1e18 + 100;
const int N = 1e2;
vector<vector< long long > > w, d;
int n, m, k;
void ResizeMatrix(vector<vector<long long> > & x)
{
    x.resize(n + 1);
    for (int i = 1; i <= n; ++ i)
    {
        x[i].resize(n + 1, oo);
    }
}
vector<vector<long long> > operator *= (vector<vector<long long> > & a, vector<vector<long long> > & b)
{
    vector<vector<long long> > c;
    ResizeMatrix(c);
    for (int i = 1; i <= n; ++ i)
    {
        for (int j = 1; j <= n; ++ j)
        {
            for (int k = 1; k <= n; ++ k)
            {
                if (a[i][k] < oo && b[k][j] < oo)
                {
                    c[i][j] = min(c[i][j], a[i][k] + b[k][j]);
                }
            }
        }
    }
    swap(a, c);
    return a;
}
void read()
{
    cin >> n >> m >> k;
    ResizeMatrix(w);
    ResizeMatrix(d);
    for (int i = 1; i <= n; ++ i)
    {
        d[i][i] = 0;
    }
    for (int i = 1; i <= m; ++ i)
    {
        int u, v;
        long long weight;
        cin >> u >> v >> weight;
        w[u][v] = min(w[u][v], weight);
    }
}
void solve()
{
    vector<vector<long long> > a = w;
    for (; k > 0; k /= 2)
    {
        if (k & 1)
            d *= a;
        a *= a;
    }
    long long ans = oo;
    for (int i = 1; i <= n; ++ i)
    {
        ans = min(ans, d[i][i]);
    }
    if (ans == oo)
    {
        cout << -1;
        return ;
    }
    cout << ans;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    freopen(TASK".INP", "r", stdin);
    freopen(TASK".OUT", "w", stdout);
    int t = 1;
    bool typetest = false;
    if (typetest)
    {
        cin >> t;
    }
    for (int __ = 1; __ <= t; ++ __)
    {
        read();
        solve();
    }
}