51nod1799-二分答案

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
#define ll long long
#define pp 1000000007

ll n;
const ll cnt[] =  
{1, 682498929, 491101308, 76479948, 723816384,  
67347853, 27368307, 625544428, 199888908, 888050723, 927880474,  
281863274, 661224977, 623534362, 970055531, 261384175, 195888993,  
66404266, 547665832, 109838563, 933245637, 724691727, 368925948,  
 268838846, 136026497, 112390913, 135498044, 217544623, 419363534,  
  500780548, 668123525, 128487469, 30977140, 522049725, 309058615,  
  386027524, 189239124, 148528617, 940567523, 917084264, 429277690,  
  996164327, 358655417, 568392357, 780072518, 462639908, 275105629,  
  909210595, 99199382, 703397904, 733333339, 97830135, 608823837,  
  256141983, 141827977, 696628828, 637939935, 811575797, 848924691,  
  131772368, 724464507, 272814771, 326159309, 456152084, 903466878,  
  92255682, 769795511, 373745190, 606241871, 825871994, 957939114,  
  435887178, 852304035, 663307737, 375297772, 217598709, 624148346,  
  671734977, 624500515, 748510389, 203191898, 423951674, 629786193,  
  672850561, 814362881, 823845496, 116667533, 256473217, 627655552,  
  245795606, 586445753, 172114298, 193781724, 778983779, 83868974,  
  315103615, 965785236, 492741665, 377329025, 847549272, 698611116};  
ll calc(ll x)
{
    ll uu=cnt[x/10000000];
    for(ll i=x/10000000*10000000+1;i<=x;i++)
    uu=uu*i%pp;
    return uu;
}
int main()
{
    ll m,k,tot=1,less_num=0,bigger_num=0;
    scanf("%lld %lld %lld",&n,&m,&k);
    ll l=1,r=n;
    while(l<=r)
    {
        ll mid=(l+r)>>1;
        if(mid<=k) less_num++,l=mid+1;else bigger_num++,r=mid-1;    
    }     
    //tot=A(m,less_num)*A((n-m+1),bigger_num);
    //tot*=(n-less_num-bigger_num)!;
     for(ll i=1;i<=less_num;i++)
         tot=(m-i+1)*tot%pp;
    for(ll i=1;i<=bigger_num;i++)
        tot=(n-m+1-i)*tot%pp;
    cout<<tot*calc(n-less_num-bigger_num)%pp<<endl;             
 }