Codechef Robot Movings

#include <algorithm>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
using namespace std;
typedef unsigned long long LL;
#define FOR(k,a,b) for(int k(a); k < (b); ++k)
#define FORD(k,a,b) for(int k(a-1); k >= (b); --k)
#define REP(k,a) for(int k=0; k < (a); ++k)
#define ABS(a) ((a)>0?(a):-(a))
typedef pair<int,int> pii;
#define x first
#define y second

int main()
{
#ifdef HOME
    freopen ("in.txt","r",stdin);
//  freopen ("out.txt","w",stdout);
#endif
    const int mSize=5001;
    const int mod=1e9+7;
    typedef int (array5k_t)[mSize];

    array5k_t* comb = new array5k_t[mSize];

    REP(i,mSize)
        comb[i][0]=1,comb[i][i]=1;
    FOR(i,1,mSize)
    FOR(j,1,i)
    {
        comb[i][j]=comb[i-1][j-1]+comb[i-1][j];
        if(comb[i][j]>=mod)
            comb[i][j]-=mod;
    }
    int N,K,K1,K2;
    LL res=0;
    while(true)
    {
        scanf("%d %d",&N,&K);
        if(N==0 && K==0)
            break;
        if(N==1 || K>2*N-3)
        {
            //because k positive
            printf("0\n");
            continue;
        }
        --K;
        K1=K/2;
        K2=(K+1)/2;
        res=2LL*comb[N-2][K1]*comb[N-2][K2];
        res%=mod;
        printf("%lld\n",res);
    }
    delete[] comb;
    return 0;
}