Buggy python submission (verdict: Time Limit Exceeded):
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

fact = [1]*(n+1)
for i in range(2,n+1):
    fact[i] = fact[i-1]*i

a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += a[i] * fact[n-i-1]//(fact[k-1]*fact[n-i-k])
    res = res%MOD

a.reverse()
for i in range(n-k+1):
    res -= a[i] * fact[n-i-1]//(fact[k-1]*fact[n-i-k])
    res = res%MOD

print(res)


Fixed submission:
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

def mpow(a, n):
    if n == 0:return 1
    if n == 1:return a%MOD
    if n%2 == 1:return (a%MOD * mpow(a, n-1)%MOD)%MOD
    t = mpow(a, n//2)
    return (t*t)%MOD

fac = [1]*(n+1)
inv_fac = [1]*(n+1)
for i in range(n):
    fac[i+1] = (fac[i]*(i+1))%MOD
inv_fac[n] = mpow(fac[n], MOD-2)
for i in range(n, 0, -1):
    inv_fac[i-1] = (inv_fac[i]*i)%MOD

def cmb(n, r):
    if n == 0 and r == 0:return 1
    if n<r or n<0:return 0
    return (fac[n]*(inv_fac[r]*inv_fac[n-r])%MOD)%MOD
 
a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
a.reverse()
for i in range(n-k+1):
    res -= (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
print(res)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

fact = [1]*(n+1)
for i in range(2,n+1):
    fact[i] = fact[i-1]*i

def cmb(n, r):
    return fact[n]//(fact[r]*fact[n-r])

a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += a[i] * fact[n-i-1]//(fact[k-1]*fact[n-i-k])

a.reverse()
for i in range(n-k+1):
    res -= a[i] * fact[n-i-1]//(fact[k-1]*fact[n-i-k])

print(res%MOD)

Fixed submission:
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

def mpow(a, n):
    if n == 0:return 1
    if n == 1:return a%MOD
    if n%2 == 1:return (a%MOD * mpow(a, n-1)%MOD)%MOD
    t = mpow(a, n//2)
    return (t*t)%MOD

fac = [1]*(n+1)
inv_fac = [1]*(n+1)
for i in range(n):
    fac[i+1] = (fac[i]*(i+1))%MOD
inv_fac[n] = mpow(fac[n], MOD-2)
for i in range(n, 0, -1):
    inv_fac[i-1] = (inv_fac[i]*i)%MOD

def cmb(n, r):
    if n == 0 and r == 0:return 1
    if n<r or n<0:return 0
    return (fac[n]*(inv_fac[r]*inv_fac[n-r])%MOD)%MOD
 
a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
a.reverse()
for i in range(n-k+1):
    res -= (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
print(res)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

fact = [1]*(n+1)
for i in range(2,n+1):
    fact[i] = fact[i-1]*i

def cmb(n, r):
    return fact[n]//(fact[r]*fact[n-r])

a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += a[i] * cmb(n-i-1, k-1)

a.reverse()
for i in range(n-k+1):
    res -= a[i] * cmb(n-i-1, k-1)

print(res%MOD)

Fixed submission:
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

def mpow(a, n):
    if n == 0:return 1
    if n == 1:return a%MOD
    if n%2 == 1:return (a%MOD * mpow(a, n-1)%MOD)%MOD
    t = mpow(a, n//2)
    return (t*t)%MOD

fac = [1]*(n+1)
inv_fac = [1]*(n+1)
for i in range(n):
    fac[i+1] = (fac[i]*(i+1))%MOD
inv_fac[n] = mpow(fac[n], MOD-2)
for i in range(n, 0, -1):
    inv_fac[i-1] = (inv_fac[i]*i)%MOD

def cmb(n, r):
    if n == 0 and r == 0:return 1
    if n<r or n<0:return 0
    return (fac[n]*(inv_fac[r]*inv_fac[n-r])%MOD)%MOD
 
a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
a.reverse()
for i in range(n-k+1):
    res -= (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
print(res)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

def cmb(n, r):
    if n - r < r: r = n - r
    if r == 0: return 1
    if r == 1: return n

    numerator = [n - r + k + 1 for k in range(r)]
    denominator = [k + 1 for k in range(r)]

    for p in range(2,r+1):
        pivot = denominator[p - 1]
        if pivot > 1:
            offset = (n - r) % p
            for k in range(p-1,r,p):
                numerator[k - offset] /= pivot
                denominator[k] /= pivot

    result = 1
    for k in range(r):
        if numerator[k] > 1:
            result *= int(numerator[k])

    return result

a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += a[i] * cmb(n-i-1, k-1)

a.reverse()
for i in range(n-k+1):
    res -= a[i] * cmb(n-i-1, k-1)

print(res%MOD)

Fixed submission:
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

def mpow(a, n):
    if n == 0:return 1
    if n == 1:return a%MOD
    if n%2 == 1:return (a%MOD * mpow(a, n-1)%MOD)%MOD
    t = mpow(a, n//2)
    return (t*t)%MOD

fac = [1]*(n+1)
inv_fac = [1]*(n+1)
for i in range(n):
    fac[i+1] = (fac[i]*(i+1))%MOD
inv_fac[n] = mpow(fac[n], MOD-2)
for i in range(n, 0, -1):
    inv_fac[i-1] = (inv_fac[i]*i)%MOD

def cmb(n, r):
    if n == 0 and r == 0:return 1
    if n<r or n<0:return 0
    return (fac[n]*(inv_fac[r]*inv_fac[n-r])%MOD)%MOD
 
a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
a.reverse()
for i in range(n-k+1):
    res -= (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
print(res)

Buggy python submission (verdict: Runtime Error):
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
from scipy.misc import comb
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()


a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += a[i] * comb(n-i-1, k-1)

a.reverse()
for i in range(n-k+1):
    res -= a[i] * comb(n-i-1, k-1)

print(res%MOD)


Fixed submission:
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

def mpow(a, n):
    if n == 0:return 1
    if n == 1:return a%MOD
    if n%2 == 1:return (a%MOD * mpow(a, n-1)%MOD)%MOD
    t = mpow(a, n//2)
    return (t*t)%MOD

fac = [1]*(n+1)
inv_fac = [1]*(n+1)
for i in range(n):
    fac[i+1] = (fac[i]*(i+1))%MOD
inv_fac[n] = mpow(fac[n], MOD-2)
for i in range(n, 0, -1):
    inv_fac[i-1] = (inv_fac[i]*i)%MOD

def cmb(n, r):
    if n == 0 and r == 0:return 1
    if n<r or n<0:return 0
    return (fac[n]*(inv_fac[r]*inv_fac[n-r])%MOD)%MOD
 
a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
a.reverse()
for i in range(n-k+1):
    res -= (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
print(res)

Buggy python submission (verdict: Runtime Error):
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
import scipy.misc
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()


a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += a[i] * scipy.misc.comb(n-i-1, k-1, exact = True)

a.reverse()
for i in range(n-k+1):
    res -= a[i] * scipy.misc.comb(n-i-1, k-1, exact = True)

print(res%MOD)


Fixed submission:
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

def mpow(a, n):
    if n == 0:return 1
    if n == 1:return a%MOD
    if n%2 == 1:return (a%MOD * mpow(a, n-1)%MOD)%MOD
    t = mpow(a, n//2)
    return (t*t)%MOD

fac = [1]*(n+1)
inv_fac = [1]*(n+1)
for i in range(n):
    fac[i+1] = (fac[i]*(i+1))%MOD
inv_fac[n] = mpow(fac[n], MOD-2)
for i in range(n, 0, -1):
    inv_fac[i-1] = (inv_fac[i]*i)%MOD

def cmb(n, r):
    if n == 0 and r == 0:return 1
    if n<r or n<0:return 0
    return (fac[n]*(inv_fac[r]*inv_fac[n-r])%MOD)%MOD
 
a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
a.reverse()
for i in range(n-k+1):
    res -= (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
print(res)

Buggy python submission (verdict: Runtime Error):
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
from scipy.misc import comb
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()


a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += a[i] * comb(n-i-1, k-1, exact = True)

a.reverse()
for i in range(n-k+1):
    res -= a[i] * comb(n-i-1, k-1, exact = True)

print(res%MOD)




Fixed submission:
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

def mpow(a, n):
    if n == 0:return 1
    if n == 1:return a%MOD
    if n%2 == 1:return (a%MOD * mpow(a, n-1)%MOD)%MOD
    t = mpow(a, n//2)
    return (t*t)%MOD

fac = [1]*(n+1)
inv_fac = [1]*(n+1)
for i in range(n):
    fac[i+1] = (fac[i]*(i+1))%MOD
inv_fac[n] = mpow(fac[n], MOD-2)
for i in range(n, 0, -1):
    inv_fac[i-1] = (inv_fac[i]*i)%MOD

def cmb(n, r):
    if n == 0 and r == 0:return 1
    if n<r or n<0:return 0
    return (fac[n]*(inv_fac[r]*inv_fac[n-r])%MOD)%MOD
 
a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
a.reverse()
for i in range(n-k+1):
    res -= (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
print(res)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()
def combinations_count(n, r):
    return math.factorial(n) // (math.factorial(n - r) * math.factorial(r))


a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += a[i] * combinations_count(n-i-1, k-1)

a.reverse()
for i in range(n-k+1):
    res -= a[i] * combinations_count(n-i-1, k-1)

print(res%MOD)

Fixed submission:
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

def mpow(a, n):
    if n == 0:return 1
    if n == 1:return a%MOD
    if n%2 == 1:return (a%MOD * mpow(a, n-1)%MOD)%MOD
    t = mpow(a, n//2)
    return (t*t)%MOD

fac = [1]*(n+1)
inv_fac = [1]*(n+1)
for i in range(n):
    fac[i+1] = (fac[i]*(i+1))%MOD
inv_fac[n] = mpow(fac[n], MOD-2)
for i in range(n, 0, -1):
    inv_fac[i-1] = (inv_fac[i]*i)%MOD

def cmb(n, r):
    if n == 0 and r == 0:return 1
    if n<r or n<0:return 0
    return (fac[n]*(inv_fac[r]*inv_fac[n-r])%MOD)%MOD
 
a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
a.reverse()
for i in range(n-k+1):
    res -= (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
print(res)

Buggy python submission (verdict: Runtime Error):
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
from scipy.special import comb
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += a[i] * comb(n-i-1, k-1, exact=True)

a.reverse()
for i in range(n-k+1):
    res -= a[i] * comb(n-i-1, k-1, exact=True)

print(res%MOD)


Fixed submission:
import sys
from math import factorial
from fractions import Fraction
import heapq, bisect, fractions
import math
import itertools
sys.setrecursionlimit(10 ** 5 + 10)
INF = 10**15 +5
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
MOD = 10**9 + 7

n, k = MAP()
a = LIST()

def mpow(a, n):
    if n == 0:return 1
    if n == 1:return a%MOD
    if n%2 == 1:return (a%MOD * mpow(a, n-1)%MOD)%MOD
    t = mpow(a, n//2)
    return (t*t)%MOD

fac = [1]*(n+1)
inv_fac = [1]*(n+1)
for i in range(n):
    fac[i+1] = (fac[i]*(i+1))%MOD
inv_fac[n] = mpow(fac[n], MOD-2)
for i in range(n, 0, -1):
    inv_fac[i-1] = (inv_fac[i]*i)%MOD

def cmb(n, r):
    if n == 0 and r == 0:return 1
    if n<r or n<0:return 0
    return (fac[n]*(inv_fac[r]*inv_fac[n-r])%MOD)%MOD
 
a.sort(reverse = True)
res = 0
for i in range(n-k+1):
    res += (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
a.reverse()
for i in range(n-k+1):
    res -= (a[i]*cmb(n-i-1, k-1))%MOD
    res = res%MOD
 
print(res)