Travelling salesman bnd do not work properly

#include<iostream>
#include<time.h>
#include<cstdlib>
#include<vector>
#include<fstream>
#define infinity 10000
#define node int
using namespace std;

void bnb(int n);
int bnbfirst(void);
int calculateLocalCost(int x,int y);

int mat[1000][1000];
int n;
int basic;
int cost=infinity;
vector<node> optimal;

int main(void)
{
    ifstream myfile2;
    myfile2.open("input6.txt");
    cout<<"Input the size of graph: "<<endl;
    myfile2>>n;

    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
            myfile2>>mat[i][j];
        }
    }

    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
            cout<<mat[i][j]<<'\t';
        }
        cout<<endl;
    }

    basic=bnbfirst();
    cout<<basic<<endl;

    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
            cout<<mat[i][j]<<'\t';
        }
        cout<<endl;
    }
    cout<<basic<<endl;;
    for(int i=0;i<optimal.size();i++)
    {
        cout<<optimal[i]<<' ';
    }cout<<endl;
}

int bnbfirst(void)
{
    int cost=0;
    for(int i=0;i<n;i++)
    {
        int low=infinity;
        for(int j=0;j<n;j++) ///lowest determined
        {
            if(mat[i][j]<low)
            {
                low=mat[i][j];
            }
        }
        for(int j=0;j<n;j++) ///low is subtracted from all elements of the row
        {
            if(mat[i][j]==infinity);
            else
            {
                mat[i][j]-=low;
            }
        }
        cost+=low;
    }

    for(int j=0;j<n;j++)
    {
        int low=infinity;
        for(int i=0;i<n;i++) ///lowest determined
        {
            if(mat[i][j]<low)
            {
                low=mat[i][j];
            }
        }
        for(int i=0;i<n;i++) ///low is subtracted from all elements of the column
        {
            if(mat[i][j]==infinity);
            else
            {
                mat[i][j]-=low;
            }
        }
        cost+=low;
        optimal.push_back(0);
    }
    return cost;
}

void bnb(int x)
{
    int localcost=infinity,next;
    for(int i=0;i<n;i++)
    {
        int flag=0;
        for(int j=0;j<optimal.size();j++)
        {
            if(i==optimal[j])
            {
                flag=1;
                break;
            }
        }
        if(flag==0)
        {
            if(localcost>calculateLocalCost(x,i))
            {
                localcost=calculateLocalCost(x,i);
                next=i;
            }
        }
    }
    basic+=localcost;
    optimal.push_back(next);

    for(int i=0;i<n;i++)
    {
        mat[x][i]=infinity;
    }
    for(int i=0;i<n;i++)
    {
        mat[i][next]=infinity;
    }
    mat[x][next]=mat[next][x]=infinity;

    int low=infinity;
    for(int i=0;i<n;i++)
    {
        if(low>mat[0][i])
        {
            low=mat[0][i];
        }
    }
    for(int i=0;i<n;i++)
    {
        mat[0][i]-=low;
    }

    bnb(next);
}

int calculateLocalCost(int x,int y)
{
    int temp[n][n];
    int low=infinity;
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
            temp[i][j]=mat[i][j];
        }
    }

    int localcost=temp[x][y];
    for(int i=0;i<n;i++)
    {
        if(temp[x][i]<low)
        {
            low=temp[x][i];
        }
    }
    localcost+=low;
}