C(n, m)模板

#include <bits/stdc++.h>
#define mp make_pair
#define pb push_back

using namespace std;

typedef pair<int, int> pii;
typedef long long ll;
typedef unsigned long long ull;

const double eps = 1e-7;
const double pi = acos(-1.0);
const int inf = 0x3f3f3f3f;

inline ll read() {
    ll f = 1, x = 0;
    char c = getchar();
    while(c < '0' || c > '9') {
        if(c == '-') f = -1;
        c = getchar();
    } 
    while(c >= '0' && c <= '9') {
        x = (x << 1) + (x << 3) + (c ^ 48);
        c = getchar();
    }
    return f * x;
}

const int mod = 1e9 + 7;
const int N = 2e6 + 10;

ll fac[N], inv[N];

ll qpow(ll a, int n) {
    ll ans = 1;
    while(n) {
        if(n & 1)   ans = (ans * a) % mod;
        a = (a * a) % mod;
        n >>= 1;
    }
    return ans;
}

ll C(int n, int m) {
    if(n < 0 || m < 0 || m > n) return 0;
    if(m == 0 || m == n)    return 1;
    return ((fac[n] * inv[m]) % mod * inv[n - m]) % mod;
}

void init() {
    fac[0] = 1;
    for(int i = 1; i < N; i++)
        fac[i] = (fac[i - 1] * i) % mod;
    inv[N - 1] = qpow(fac[N - 1], mod - 2);
    for(int i = N - 2; i >= 0; i--)
        inv[i] = (inv[i + 1] * (i + 1)) % mod;
}


int main() {
    // freopen("in.txt", "r", stdin);
    // freopen("out.txt", "w", stdout);
    // ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
    init();
    while(true) {
        int n = read(), m = read();
        printf("%lld\b", C(n, m));
    }
    return 0;
}