Buggy python submission (verdict: Time Limit Exceeded):
from math import factorial

n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))
s=0

#maxについて
for i in range(k-1,n):
	s+=(a[i]*factorial(i)//factorial(k-1)//factorial(i-k+1))%(10**9+7)
	s%=10**9+7
for i in range(n-k+1):
	s-=(a[i]*factorial(n-i-1)//factorial(k-1)//factorial(n-k-i))%(10**9+7)
	s%=10**9+7
print(s)


Fixed submission:
def cmb(n, k, mod, fac, ifac):
    """
    nCkを計算する
    """
    k = min(k, n-k)
    return fac[n] * ifac[k] * ifac[n-k] % mod


def make_tables(mod, n):
    """
    階乗テーブル、逆元の階乗テーブルを作成する
    """
    fac = [1, 1] # 階乗テーブル・・・(1)
    ifac = [1, 1] #逆元の階乗テーブル・・・(2)
    inverse = [0, 1] #逆元テーブル・・・(3)

    for i in range(2, n+1):
        fac.append((fac[-1] * i) % mod)
        inverse.append((-inverse[mod % i] * (mod//i)) % mod)
        ifac.append((ifac[-1] * inverse[-1]) % mod)
    return fac, ifac
    
n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))
MOD=10**9+7

fac, ifac=make_tables(MOD,n)

s=0
for i in range(k-1,n):
	s+=(a[i]-a[n-i-1])*cmb(i,k-1,MOD,fac,ifac)
	s%=10**9+7
print(s)

Buggy python submission (verdict: Time Limit Exceeded):
n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))

s=0
cmb=1
for i in range(k-1,n):
	s+=(a[i]-a[n-i-1])*cmb
	s%=10**9+7
	cmb=cmb*(i+1)//(i-k+2)
print(s)

Fixed submission:
def cmb(n, k, mod, fac, ifac):
    """
    nCkを計算する
    """
    k = min(k, n-k)
    return fac[n] * ifac[k] * ifac[n-k] % mod


def make_tables(mod, n):
    """
    階乗テーブル、逆元の階乗テーブルを作成する
    """
    fac = [1, 1] # 階乗テーブル・・・(1)
    ifac = [1, 1] #逆元の階乗テーブル・・・(2)
    inverse = [0, 1] #逆元テーブル・・・(3)

    for i in range(2, n+1):
        fac.append((fac[-1] * i) % mod)
        inverse.append((-inverse[mod % i] * (mod//i)) % mod)
        ifac.append((ifac[-1] * inverse[-1]) % mod)
    return fac, ifac
    
n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))
MOD=10**9+7

fac, ifac=make_tables(MOD,n)

s=0
for i in range(k-1,n):
	s+=(a[i]-a[n-i-1])*cmb(i,k-1,MOD,fac,ifac)
	s%=10**9+7
print(s)

Buggy python submission (verdict: Time Limit Exceeded):
n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))

s=0
cmb=1
for i in range(k-1,n):
	s+=(a[i]-a[n-i-1])*cmb
	s%=10**9+7
	cmb=cmb*(i+1)//(i-k+2)
print(s)

Fixed submission:
def cmb(n, k, mod, fac, ifac):
    """
    nCkを計算する
    """
    k = min(k, n-k)
    return fac[n] * ifac[k] * ifac[n-k] % mod


def make_tables(mod, n):
    """
    階乗テーブル、逆元の階乗テーブルを作成する
    """
    fac = [1, 1] # 階乗テーブル・・・(1)
    ifac = [1, 1] #逆元の階乗テーブル・・・(2)
    inverse = [0, 1] #逆元テーブル・・・(3)

    for i in range(2, n+1):
        fac.append((fac[-1] * i) % mod)
        inverse.append((-inverse[mod % i] * (mod//i)) % mod)
        ifac.append((ifac[-1] * inverse[-1]) % mod)
    return fac, ifac
    
n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))
MOD=10**9+7

fac, ifac=make_tables(MOD,n)

s=0
for i in range(k-1,n):
	s+=(a[i]-a[n-i-1])*cmb(i,k-1,MOD,fac,ifac)
	s%=10**9+7
print(s)

Buggy python submission (verdict: Time Limit Exceeded):
n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))

from operator import mul
from functools import reduce

def cmb(n,r):
    r = min(n-r,r)
    if r == 0: return 1
    over = reduce(mul, range(n, n - r, -1))
    under = reduce(mul, range(1,r + 1))
    return over // under

s=0
#maxについて
for i in range(k-1,n):
	s+=a[i]*cmb(i,k-1)
	s%=10**9+7
for i in range(n-k+1):
	s-=a[i]*cmb(n-i-1,k-1)
	s%=10**9+7
print(s)

Fixed submission:
def cmb(n, k, mod, fac, ifac):
    """
    nCkを計算する
    """
    k = min(k, n-k)
    return fac[n] * ifac[k] * ifac[n-k] % mod


def make_tables(mod, n):
    """
    階乗テーブル、逆元の階乗テーブルを作成する
    """
    fac = [1, 1] # 階乗テーブル・・・(1)
    ifac = [1, 1] #逆元の階乗テーブル・・・(2)
    inverse = [0, 1] #逆元テーブル・・・(3)

    for i in range(2, n+1):
        fac.append((fac[-1] * i) % mod)
        inverse.append((-inverse[mod % i] * (mod//i)) % mod)
        ifac.append((ifac[-1] * inverse[-1]) % mod)
    return fac, ifac
    
n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))
MOD=10**9+7

fac, ifac=make_tables(MOD,n)

s=0
for i in range(k-1,n):
	s+=(a[i]-a[n-i-1])*cmb(i,k-1,MOD,fac,ifac)
	s%=10**9+7
print(s)

Buggy python submission (verdict: Time Limit Exceeded):
from math import factorial

n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))

fact=[factorial(i) for i in range(n)]
s=0
#maxについて
for i in range(k-1,n):
	s+=a[i]*fact[i]//fact[k-1]//fact[i-k+1]
	s%=10**9+7
for i in range(n-k+1):
	s-=a[i]*fact[n-i-1]//fact[k-1]//fact[n-k-i]
	s%=10**9+7
print(s)

Fixed submission:
def cmb(n, k, mod, fac, ifac):
    """
    nCkを計算する
    """
    k = min(k, n-k)
    return fac[n] * ifac[k] * ifac[n-k] % mod


def make_tables(mod, n):
    """
    階乗テーブル、逆元の階乗テーブルを作成する
    """
    fac = [1, 1] # 階乗テーブル・・・(1)
    ifac = [1, 1] #逆元の階乗テーブル・・・(2)
    inverse = [0, 1] #逆元テーブル・・・(3)

    for i in range(2, n+1):
        fac.append((fac[-1] * i) % mod)
        inverse.append((-inverse[mod % i] * (mod//i)) % mod)
        ifac.append((ifac[-1] * inverse[-1]) % mod)
    return fac, ifac
    
n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))
MOD=10**9+7

fac, ifac=make_tables(MOD,n)

s=0
for i in range(k-1,n):
	s+=(a[i]-a[n-i-1])*cmb(i,k-1,MOD,fac,ifac)
	s%=10**9+7
print(s)

Buggy python submission (verdict: Time Limit Exceeded):
from math import factorial

n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))
s=0

#maxについて
for i in range(k-1,n):
	s+=a[i]*factorial(i)//factorial(k-1)//factorial(i-k+1)
	s%=10**9+7
for i in range(n-k+1):
	s-=a[i]*factorial(n-i-1)//factorial(k-1)//factorial(n-k-i)
	s%=10**9+7
print(s)

Fixed submission:
def cmb(n, k, mod, fac, ifac):
    """
    nCkを計算する
    """
    k = min(k, n-k)
    return fac[n] * ifac[k] * ifac[n-k] % mod


def make_tables(mod, n):
    """
    階乗テーブル、逆元の階乗テーブルを作成する
    """
    fac = [1, 1] # 階乗テーブル・・・(1)
    ifac = [1, 1] #逆元の階乗テーブル・・・(2)
    inverse = [0, 1] #逆元テーブル・・・(3)

    for i in range(2, n+1):
        fac.append((fac[-1] * i) % mod)
        inverse.append((-inverse[mod % i] * (mod//i)) % mod)
        ifac.append((ifac[-1] * inverse[-1]) % mod)
    return fac, ifac
    
n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))
MOD=10**9+7

fac, ifac=make_tables(MOD,n)

s=0
for i in range(k-1,n):
	s+=(a[i]-a[n-i-1])*cmb(i,k-1,MOD,fac,ifac)
	s%=10**9+7
print(s)

Buggy python submission (verdict: Runtime Error):
from math import factorial

n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))
s=0

for i in range(n-k+1):
	for j in range(i+k-1,n):
		s+=(a[j]-a[i])*factorial(j-i-1)//factorial(k-2)//factorial(j-i-k+1)
		s%=10**9+7
print(s)

Fixed submission:
def cmb(n, k, mod, fac, ifac):
    """
    nCkを計算する
    """
    k = min(k, n-k)
    return fac[n] * ifac[k] * ifac[n-k] % mod


def make_tables(mod, n):
    """
    階乗テーブル、逆元の階乗テーブルを作成する
    """
    fac = [1, 1] # 階乗テーブル・・・(1)
    ifac = [1, 1] #逆元の階乗テーブル・・・(2)
    inverse = [0, 1] #逆元テーブル・・・(3)

    for i in range(2, n+1):
        fac.append((fac[-1] * i) % mod)
        inverse.append((-inverse[mod % i] * (mod//i)) % mod)
        ifac.append((ifac[-1] * inverse[-1]) % mod)
    return fac, ifac
    
n,k=map(int,input().split())
a=sorted(list(map(int, input().split())))
MOD=10**9+7

fac, ifac=make_tables(MOD,n)

s=0
for i in range(k-1,n):
	s+=(a[i]-a[n-i-1])*cmb(i,k-1,MOD,fac,ifac)
	s%=10**9+7
print(s)