Submission #19698

#	TimeUTC-0	Username	Problem	Language	Result	Execution time	Memory
19698	2016-02-25 04:41:36	Namnamseo	순열 (kriii4_T)	C++14	8 / 100	2000 ms	16708 KiB

T

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#include<cstdio>
long long mans,c,mul[1000003],fac[1000003],a,b,i,j,s=1,ans,X=1e9+7;
main()
{
    scanf("%lld%lld",&a,&b);
    if(b>=a)
    {
        printf("0");return 0;
    }
    for(;b<=a-1;){
    b++;ans=0;
    mul[a-b+1]=1;
    for(i=a-b;i>=1;i--)
    {
        mul[i]=mul[i+1]*i%X;
    }
    fac[0]=1;
    for(i=1;i<=a;i++)fac[i]=fac[i-1]*i%X;
    for(i=1;i<=a&&a-i>=0&&a-b+2-i>=1;i++)
    {
        ans+=i*b%X*fac[a-i]%X*mul[a-b+2-i]%X;
        ans%=X;
    }
    mans+=ans*(a-b+1)%X;
    mans%=X;
    }
    printf("%lld",mans);
}
 
 
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• Subtask 1: 8 / 8
• Subtask 2: 0 / 92