private static final long MOD = 1000000007;
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer st = new StringTokenizer(br.readLine(), " ");
long n = Long.parseLong(st.nextToken());
long k = Long.parseLong(st.nextToken());
long numerator = factorial(n);
long denominator = factorial(k) * factorial(n - k) % MOD;
long result = numerator * modInverse(denominator, MOD - 2) % MOD;
System.out.println(result);
}
private static long factorial(long num) {
long result = 1;
for (long i = 2; i <= num; i++) {
result = (result * i) % MOD;
}
return result;
}
private static long modInverse(long base, long exp) {
long result = 1;
while (exp > 0) {
if (exp % 2 == 1) {
result = (result * base) % MOD;
}
base = (base * base) % MOD;
exp /= 2;
}
return result;
}
출처:https://www.acmicpc.net/problem/11401
