Dijktra_main

#include <iostream>
#include <fstream>

using namespace std;

int main ()
{
    int a , b, n , i , sum = 0;
    fstream f;
    f.open("inputDijktra.txt");
    f >> n;
    f >> a;
    f >> b;
    int G[n][n] , len[n] , S[n] , P[n];
    int k = 0 , j = 0;
//  cout << n << " " << a << " "<< b;
//  Creat
    for (int i = 0 ; i < n ; i++)
    {
        for (int j = 0; j < n ; j++)

        {
            f >> G[i][j];
            sum += G[i][j];
        }

    }

    for (int i = 0 ; i < n ; i++)
    {
        for (int j = 0; j < n ; j++)

        {
            if (i != j && !G[i][j]) G[i][j] = sum;
        }
    }
    a--;
    b--;
    for (int i = 0 ; i < n ; i++)
    {
        len[i] = sum;
        S[i] = a;
        P[i] = 0;
    }
    len [a] = 0;

//Dijktra
    while (!P[b])
    {
    //tim mot vi tri ko phai la vo cung
    for (i = 0 ; i < n ; i++)
        if (!P[i] && len[i] < sum)
            break;

    if (i >= n)
    {
    cout << "Not exist the path " << a << " - > " << b << endl ; break;
    }
    // tim diem co do dai la min
    for (int j = 0 ; j < n ; j++)
        if (!P[j] && len[i] > len[j])
            i = j;

    //cho i vao danh sach xet
    P[i] = 1;

    //tinh lai cac dinh chua xet
    for (int j = 0 ; j < n ; j++)
        if (!P[j] && len[i] + G[i][j] < len[j])
            len[j] = len[i] + G[i][j], S[j] = i;

    }
    cout << "Done Dijktra !" << endl;

    if (len[b] > 0 && len[b] < sum)
    {
    cout << "The Min Length from " << a + 1<< " to " << b + 1 <<" is " << len[b] << endl;
    //truy vet
    while (i != a)
    {
        cout << i + 1<< " <- ";
        i = S[i];
    }
    cout << a + 1;
    }
    else cout << "Not Exist the path from " << a << " to " << b <<  endl;
    return 0;
}