代码

#include <algorithm>
#include <cstring>
#include <iostream>

using namespace std;

const int N = 210, INF = 1e9;

int n, m, Q;
int d[N][N];

void floyd()
{
    for (int k = 1; k <= n; k++) {
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= n; j++) {
                d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
            }
        }
    }
}

int main()
{
    cin >> n >> m >> Q;

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            if (i == j) {
                d[i][j] = 0;
            }
            else {
                d[i][j] = INF;
            }
        }
    }
    while (m--) {
        int a, b, c;
        cin >> a >> b >> c;
        d[a][b] = min(d[a][b], c);
    }

    floyd();

    while (Q--) {
        int a, b;
        cin >> a >> b;

        int t = d[a][b];
        if (t > INF / 2) {
            cout << "impossible" << endl;
        }
        else {
            cout << t << endl;
        }
    }
    return 0;
}