Johnson version2

//johnson
#include<iostream>
#include<fstream>
#include<vector>
#include<queue>
#include<functional>
#define INF 990
using namespace std;

typedef pair<int, int> p;
vector<vector<int>> g;
vector<int> dist;
int n, m;
void read()
{
	ifstream in("file.txt");
	if (!in.is_open())
		cout << "error";
	else
	{
		in >> n >> m;
		g.resize(n + 1);
		for (int i = 0; i <= n; i++)
			g[i].assign(n + 1, 0);
		int x, y, w;
		dist.assign(n + 1, INF);
		for (int i = 0; i < m; i++)
		{
			in >> x >> y >> w;
			g[x][y] = w;
		}
	}
}
void change_matrix()
{
	g.resize(n + 1);
	for (int i = 0; i <= n; i++)
	{
		g[0][i] = 0;
		g[i][0] = 0;
	}
}
bool belman(int source)
{
	dist.assign(n + 1 , INF);
	dist[source] = 0;
	for(int i=1;i<=n;i++)
		for(int j=1;j<=n;j++)
			for (int k = 1; k <= n; k++)
				if (dist[j] != INF)
					if(g[j][k]!=0 && dist[k]> dist[j]+g[j][k])
						dist[k] = dist[j] + g[j][k];
	//checking for negative cycles
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= n; j++)
			if (g[i][j] != 0 && dist[i] > dist[j] + g[i][j])
				return false;
	return true;

}

void dijkstra(int source)
{
	priority_queue <int, vector<int>, greater<int>> q;
	dist[source] = 0;
	q.push(source );
	while (!q.empty())
	{
		int i = q.top();
		q.pop();
		for (int j = 1; j <= n; j++)
		{
			if (g[i][j] != 0 && dist[i] > dist[j] + g[i][j])
			{
				dist[i] = dist[j] + g[i][j];
				q.push(j );
			}
		}
	}
}
void johnson(int source)
{
	change_matrix();
	if (belman(source))
	{
		for (int i = 1; i < n; i++)
			for (int j = 1; j < n; j++)
				g[i][j] += dist[i] - dist[j];

		dist.assign(n + 1, INF);
		dist[source] = 0;
		dijkstra(source);
	}
	else
		cout << "contains negative cycles\n";
}
int main()
{
	read();
	int source = 1;
	johnson(source);
	cout << "minimum distance between " << source << " and every node:\n";
	for (int i = 1; i < n; i++)
		cout << "node:" << i << " distance:" << dist[i] << endl;
	return 0;
}