Submission #19993

#	TimeUTC-0	Username	Problem	Language	Result	Execution time	Memory
19993	2016-02-25 08:13:48	xdoju	괄호 (kriii4_R)	C++14	100 / 100	604 ms	1084 KiB

R

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#include <stdio.h>
const int MOD = 1000000007;
int mul(int x, int y){ return (long long)x * y % MOD; }
int power(int x, int y){
  if(y == 0) return 1;
  int r = power(x, y / 2);
  r = mul(r, r);
  if(y % 2 == 1) r = mul(r, x);
  return r;
}
int modinv(int x){ return power(x, MOD - 2); }
int main(){
  int N, K; scanf("%d%d", &N, &K);
  int ans = 0, v = power(K, N);
  for(int op = N; op >= 0; op--){
    int cl = N - op;
    if(cl > op) break;
    ans += v; ans %= MOD;
    v = mul(v, modinv(K));
    v = mul(v, N - cl * 2 - 1);
    v = mul(v, modinv(cl + 1));
 
 
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• Subtask 1: 8 / 8
• Subtask 2: 92 / 92