题解（包AC）

#include <bits/stdc++.h>
using namespace std;

const int INF = 0x3f3f3f3f;
const int N = 210;
int dis[N][N];

int main() {
    int n, m, K;
    cin >> n >> m >> K;

    // 初始化邻接矩阵
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= n; ++j) {
            if (i == j) dis[i][j] = 0;
            else dis[i][j] = INF;
        }
    }

    // 读取边
    for (int i = 1; i <= m; ++i) {
        int x, y, z;
        cin >> x >> y >> z;
        dis[x][y] = z;
    }

    // Floyd-Warshall 算法
    for (int k = 1; k <= n; ++k)
        for (int i = 1; i <= n; ++i)
            for (int j = 1; j <= n; ++j)
                if (dis[i][k] != INF && dis[k][j] != INF)
                    dis[i][j] = min(dis[i][j], dis[i][k] + dis[k][j]);

    // 处理查询
    while (K--) {
        int a, b;
        cin >> a >> b;
        if (dis[a][b] == INF) cout << "impossible" << endl;
        else cout << dis[a][b] << endl;
    }

    return 0;
}