Detachment - HDU 5976

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<cmath>
#include<iostream>
using namespace std;
#define maxn 50000
const int mod = 1e9+7;
typedef __int64 LL;
LL sum[maxn];
LL mu[maxn];

void init()
{
    mu[1]=1;
    for(int i=2; i<maxn; i++)
    {
        sum[i]=sum[i-1]+i;
        mu[i]=(mu[i-1]*i)%mod;
    }
    sum[1]=1;
}

LL mult(LL a,int n) // 快速幂
{
    LL ans=1;
    while(n)
    {
        if(n&1)ans=(ans*a)%mod;
        a=(a*a)%mod;
        n>>=1;
    }
    return ans;
}

int main()
{
    init();
    int T;
    scanf("%d",&T);
    while(T--)
    {
        LL x;
        scanf("%I64d",&x);
        int index=lower_bound(sum,sum+maxn,x)-sum;
        LL ans;
        if(sum[index]==x)
            ans=mu[index];
        else
        {
            if(sum[index]==x+1)
                ans=((mu[index+1]*mult(index,mod-2))%mod*mult(2,mod-2))%mod;
            else
                ans=(mu[index]*mult(sum[index]-x,mod-2))%mod;
        }
        printf("%I64d\n",ans);
    }
    return 0;
}