Light OJ 1102

#include<bits/stdc++.h>
using namespace std;
typedef int LL;
const int maxn = 2000000 + 131;
const LL MOD = 1000000007;

LL Mul(LL a, LL b, LL m)
{
    a = (a % m + m) % m;
    b = (b % m + m) % m;
    LL ret = 0;
    while(b)
    {
        if(b & 1) ret = (ret + a) % m;
        b >>= 1;
        a <<= 1;
        a %= m;
    }
    return ret;
}

LL Pow_Mod(LL a, LL n, LL m)
{
    LL ret = 1;
    while(n)
    {
        if(n & 1) ret = Mul(ret, a, m);
        n >>= 1;
        a = Mul(a, a, m);
    }
    return ret;
}

LL Num[maxn], Inv[maxn];
void Init()
{
    Num[0] = 1;
    for(LL i = 1; i < maxn; ++i) Num[i] = Mul(Num[i-1], i, MOD);
    Inv[maxn-1] = Pow_Mod(Num[maxn-1], MOD-2, MOD);
    for(LL i = maxn-2; i >= 0; --i) Inv[i] = Mul(Inv[i+1], (i+1), MOD);
}

LL C(LL m, LL n, LL mod)
{
    if(n == 0 || n == m) return 1;
    LL ret = 1;
    LL s = m - n;
    ret = Mul(Num[m], Inv[s], mod);
    ret = Mul(ret, Inv[n], mod);
    return ret;
}

int main()
{
    Init();
    int t;
    LL n, k;
    scanf("%d",&t);
    for(int kase = 1; kase <= t; ++kase)
    {
        scanf("%d %d",&n, &k);
        printf("Case %d: %d\n",kase, C(n+k-1, k-1, MOD));
    }
}