01 January Count even length(T)

class Solution{

public:

int inv(int n, int m, int mod=1000000007){

if(m==0) return 1;

if(m&1) return (n*1ll*inv(n, m-1))%mod;

int tmp=inv(n, m/2);

return (tmp*1ll*tmp)%mod;

}

int compute_value(int n)

{

// Code here

int m = 1000000007;

long long fact2N=1, factN;

for(int i=1; i<=2*n; i++){

fact2N *= i;

fact2N %= m;

if(i==n)factN=fact2N;

}

factN = (factN*factN)%m;

return (fact2N * 1ll * inv(factN, m-2))%m;

}

};