Floyd-Warshall算法其实是比较容易理解也比较容易coding的DP... 不说了，上代码：

#include <cmath>
#include <cstdio>
#include <vector>
#include <map>
#include <set>
#include <unordered_set>
#include <string>
#include <iostream>
#include <algorithm>
using namespace std;

int main() 
{
    //    Get input
    int n, m; cin >> n >> m;

    const int INVALID = std::numeric_limits<int>::max();
    vector<vector<int>> mat(n, vector<int>(n, INVALID));
    for (int i = 0; i < n; i++)
        mat[i][i] = 0;
    while (m--)
    {
        int i, j, len;
        cin >> i >> j >> len;
        mat[i - 1][j - 1] = std::min(mat[i - 1][j - 1], len);
        mat[j - 1][i - 1] = mat[i - 1][j - 1];
    }

    //    Floyd-Warshall
    for (int k = 0; k < n; k ++)
    for (int i = 0; i < n; i ++)
    for (int j = 0; j < n; j++)
    {
        if (i != j && i != k && j != k)
        {
            if (mat[i][k] != INVALID &&
                mat[k][j] != INVALID)
                mat[i][j] = std::min(mat[i][j], mat[i][k] + mat[k][j]);
        }
    }

    //    Output
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            cout << mat[i][j] << " ";
        }
        cout << endl;
    }
    return 0;
}