Floyd

思想

• 遍历所有V，考虑让每个顶点介入每个路径，以更新路径

题目

代码

#include <bits/stdc++.h>
using namespace std;
const int N = 210;
const int inf = 0x3f3f3f3f;
int g[N][N];
int n, m, k;
void floyd()
{for(int t = 1; t <= n; t++){for(int i = 1; i <= n; i++){for(int j = 1; j <= n; j++){g[i][j] = min(g[i][j], g[i][t] + g[t][j]);}}}
}
int main()
{cin >> n >> m >> k;for(int i = 1; i <= n; i++){for(int j = 1; j <= n; j++){if(i == j) g[i][j] = 0;else g[i][j] = inf;}}for(int i = 1; i <= m; i++){int a, b, c;cin >> a >> b >> c;g[a][b] = min(g[a][b], c);}floyd();while(k--){int a, b;cin >> a >> b;if(g[a][b] > inf / 2) cout << "impossible\n" ;else cout << g[a][b] << '\n';}}