Giving TLE , why, please explain?

#1

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

#define ll long long
#define nL “\n”
#define pb push_back

ll p;
ll k;
vector b, c;

vector<vector> multiply(vector<vector> A, vector<vector> B)
{
vector<vector> C(k + 2, vector(k + 2)); // matrix multiplication (A * B) => store in C

for (int i = 1; i <= k+1; i++)
{
	for (int j = 1; j <= k+1; j++)
	{
		for (int x = 1; x <= k+1; x++)
		{
			C[i][j] = (C[i][j] + (A[i][x] * B[x][j]) % p) % p;
		}
	}
}
return C;

}

vector<vector> power(vector<vector> A, int p)
{
if (p == 1)
return A;

if (p & 1) //odd
{
	return multiply(A, power(A, p - 1));
}

vector<vector<ll>> X = power(A, p / 2);     //even
return multiply(X, X);

}

ll compute(ll n)
{
if (n == 0)
return 0;

if (n <= k)
	return b[n - 1];

// step 1  find F1(stores first k terms)
vector<ll> F1(k + 2);
F1[1] = 0;
for (int i = 2; i <= k+1; i++)
{
	F1[i] = b[i - 2];
}

//step2 - compute T(transformation matrix)
vector<vector<ll>> T(k + 2, vector<ll>(k + 2));

for (int i = 1; i <= k+1; i++)
{
	for (int j = 1; j <= k+1; j++)
	{
		if(i == 1 && j == 1)
        {
            T[i][j] = 1;
            continue;
        }

        if(i == k+1 && j > 1)
        {
            T[i][j] = c[k - j + 1];
            continue;
        }

        if(j == i+1)
        {
            T[i][j] = 1;
        }
        else
           T[i][j] = 0;
	}
}


//step3 - cal T ^ n
T = power(T, n);

//step 4 - cal res by T^n-1 * F1
ll res = 0;
for (int i = 1; i <= k+1; i++)
{
	res = (res + (T[1][i] * F1[i]) % p) % p;
}
return res;

}

int32_t main()
{
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);

ll t, n, num;

cin >> t;
while (t--)
{
	cin >> k;

	for (int i = 1; i <= k; i++)
	{
		cin >> num;
		b.pb(num);
	}

	for (int i = 1; i <= k; i++)
	{
		cin >> num;
		c.pb(num);
	}
    
    ll m, n;
	cin >> m >> n >> p;

	ll Sn = compute(n);
    ll Sm1 = compute(m-1);

    ll reqSum = (Sn - Sm1 + p) % p;
    cout << reqSum << nL;

	b.clear();
	c.clear();
}

return 0;

}

#2

@devang_11912089,

  1. In the power function, the datatype of p is int instead of ll, which will cause overflow issues.
    vector<vector<ll>> power(vector<vector<ll>> A, ll p)

  2. If n<=k, you are just returning b[n-1].

if (n <= k){
ll sum = 0;
for(int i=0;i<n;i++){
sum += b[i];
}
return sum;
}

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#3

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