最短路算法-floyd算法

19 Jun 2023 in Algorithm Pageviews

use floyd easily!

多源汇最短路常用算法—-Floyd算法

Floyd求最短路

#include <bits/stdc++.h>

using namespace std;
class Solution {
public:
    int floyd(int n)
    {
        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()
{
    constexpr int N = 210;
    constexpr int INF = 0x3f3f3f3f;
    int d[N][N];
    int n = 0, m = 0, q = 0;
    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, w;
        cin >> a >> b >> w;
        d[a][b] = min(d[a][b], w);
    }
    sol.floyd(n);
    while (q--) {
        int a = 0, b = 0;
        cin >> a >> b;
        if (d[a][b] > INF / 2) {
            cout << -1 << endl;
        } else {
            cout << d[a][b] << endl;
        }
    }
    return 0;
}