Submission #2971851

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Source Code Expand

#include<iostream>
#include<cstdio>

using namespace std;

const long long P=1000000007ll;
long long n,k,f[10001];

long long qpow(long long a,int x){
	if(x<0)return 1;
	long long s=1ll;
	while(x){if(x&1)(s*=a)%=P;(a*=a)%=P;x>>=1;}
	return s;
}

int main(){
	scanf("%lld%lld",&n,&k);
	f[0]=1ll;
	for(int i=1;i<n;++i){for(int j=i;j;--j)f[j]=(f[j+1]+f[j-1])%P;f[0]=f[1];}
	printf("%lld",f[n-k]*qpow(2ll,n-k-1)%P);
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:17:25: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%lld%lld",&n,&k);
                         ^

Judge Result