I was solving this its problem on perfect matching in a graph.I have to tell whether a graph can be perfect matched.I used tutte matrix and Gaussian elimination method to find whether a perfect matching exists but i don't know why my code doesn't works , please help!

#include "bits/stdc++.h"
using namespace std;

#define ll long long
#define mod 10000+7
#define MAX 101
ll r,i,j,k;

ll lcm(ll x,ll y)
{
    ll t;
    while (y != 0)
    {
      t=y;
      y=x%y;
      x=t;
    }
    return x;
}
ll random_number_generator()
{
	// Declare variable to hold seconds on clock.

time_t seconds;

// Get value from system clock and
// place in seconds variable.

time(&seconds);

// Convert seconds to a unsigned
// integer.

srand((unsigned ll) seconds);

// Output random values.

return (rand()+mod) % mod;
}

ll det(ll a[101][101]) /*this code converts mtrix to upper triangle so dterminant can be found by taking product of just diagonal elements*/
{ll l,d1,d2;
 for(i=0;i<r-1;i++)
       {
           for(j=i+1;j<r;j++)
           {
             l=lcm(a[i][i],a[j][i]);
             if(l!=0&&(a[i][i]!=0&&a[j][i]!=0))
             {
               l=(a[i][i]*a[j][i])/l;
               d1=l/a[i][i];
               d2=l/a[j][i];
               a[j][i]=0;
               for(k=i+1;k<r;k++)
               {
                 a[j][k]=(d2*a[j][k])-(d1*a[i][k]);
               }
             }
           }
        }
        ll p =1;
        for(int i = 0 ;i < r; i++)
        {
        	
        	p = (p * a[i][i]+mod)%mod;
        	p = (p * a[i][r-1-i] + mod)%mod;
        }
        return p;
} 

int main(int argc, char const *argv[])
{
	ll t;
	cin >> t;

	while(t--)
	{
		ll n , m;
		cin >> n >> m;

		r=n;
ll a[101][101];

		for(ll i = 0; i <= n; i++)
		{
			for(ll j = 0; j <= n; j++)
				a[i][j] = 0;
		}

		ll rnd = random_number_generator();

		while(m--)
		{
			ll x , y;
			cin >> x >> y;
			x--;y--;
			ll rnd = random_number_generator();

			if(x < y)
				a[x][y] = (rnd);
			else if(x > y)
				a[x][y] = (-rnd);

			a[y][x] = -a[x][y];
		}

		ll dete = det(a);

		if(dete == 0)
			cout << "NO" << endl;
		else
			cout << "YES" << endl;
	}
	return 0;
}