Buggy python submission (verdict: Runtime Error):
# import math
# import fractions
# import numpy as np
from scipy.misc import comb

MOD = 10 ** 9 + 7

# ゼロ埋め
# list = [0] * N

# 二次元配列
# [[inf, inf, inf], [inf, inf, inf]]
# dp = [[float('inf')] * (H + 1) for i in range(N + 1)]

def cmb(n, r, p):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % p
 
p = 10 ** 9 + 7
fact = [1, 1]
factinv = [1, 1]
inv = [0, 1]
 
for i in range(2, N + 1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    factinv.append((factinv[-1] * inv[-1]) % p)

def solve(N, M, A):
    max = 0
    desc = sorted(A, reverse=True)

    for i in range(1, N):
        max += desc[i] * comb(N-i,  M-1, MOD)

    min = 0
    asc = sorted(A)
    for i in range(1, N):
        min += desc[i] * comb(N-i,  M-1, NOD)

    return int((max - min) % MOD)

# S = input()
# N = int(input())
N, M = map(int, input().split())
A = list(map(int, input().split()))
# B = [int(input()) for _ in range(n)]
# A = []
# B = []
# for _ in range(N):
#     a, b = list(map(int, input().split()))
#     A.append(a)
#     B.append(b)

print(solve(N, M, A))


Fixed submission:
MOD = 10 ** 9 + 7

def solve(N, K, A):
    A.sort()
    ans = 0
 
    for i in range(1, N):
        now = cmb(i, K - 1, MOD)
        ans += A[i] * now
 
    A.sort(reverse=True)
    for i in range(1, N):
        now = cmb(i, K - 1, MOD)
        ans += A[i] * (-now)
 
    return ans % MOD
 
 
# N = int(input())
# S = input()
N, K = map(int, input().split())
A = list(map(int, input().split()))

def cmb(n, r, p):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % p

p = 10 ** 9 + 7
fact = [1, 1]
factinv = [1, 1]
inv = [0, 1]
 
for i in range(2, N + 1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    factinv.append((factinv[-1] * inv[-1]) % p)


print(solve(N, K, A))

Buggy python submission (verdict: Runtime Error):
# import math
# import fractions
# import numpy as np
from scipy.misc import comb

MOD = 10 ** 9 + 7

# ゼロ埋め
# list = [0] * N

# 二次元配列
# [[inf, inf, inf], [inf, inf, inf]]
# dp = [[float('inf')] * (H + 1) for i in range(N + 1)]

def solve(N, M, A):
    max = 0
    desc = sorted(A, reverse=True)

    for i in range(N):
        max += desc[i] * comb(N-i-1,  M-1)

    min = 0
    asc = sorted(A)
    for i in range(N):
        min += asc[i] * comb(N-i-1,  M-1)

    return int((max - min) % MOD)

# S = input()
# N = int(input())
N, M = map(int, input().split())
A = list(map(int, input().split()))
# B = [int(input()) for _ in range(n)]
# A = []
# B = []
# for _ in range(N):
#     a, b = list(map(int, input().split()))
#     A.append(a)
#     B.append(b)

print(solve(N, M, A))


Fixed submission:
MOD = 10 ** 9 + 7

def solve(N, K, A):
    A.sort()
    ans = 0
 
    for i in range(1, N):
        now = cmb(i, K - 1, MOD)
        ans += A[i] * now
 
    A.sort(reverse=True)
    for i in range(1, N):
        now = cmb(i, K - 1, MOD)
        ans += A[i] * (-now)
 
    return ans % MOD
 
 
# N = int(input())
# S = input()
N, K = map(int, input().split())
A = list(map(int, input().split()))

def cmb(n, r, p):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % p

p = 10 ** 9 + 7
fact = [1, 1]
factinv = [1, 1]
inv = [0, 1]
 
for i in range(2, N + 1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    factinv.append((factinv[-1] * inv[-1]) % p)


print(solve(N, K, A))

Buggy python submission (verdict: Runtime Error):
MOD = 10 ** 9 + 7

def solve(N, K, A):
    A.sort()
    ans = 0
 
    for i in range(1, N):
        now = comb(i, K - 1, MOD)
        ans += A[i] * now
 
    A.sort(reverse=True)
    for i in range(1, N):
        now = comb(i, K - 1, MOD)
        ans += A[i] * (-now)
 
    return ans % MOD
 
 
# N = int(input())
# S = input()
N, K = map(int, input().split())
A = list(map(int, input().split()))

def cmb(n, r, p):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % p

p = 10 ** 9 + 7
fact = [1, 1]
factinv = [1, 1]
inv = [0, 1]
 
for i in range(2, N + 1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    factinv.append((factinv[-1] * inv[-1]) % p)


print(solve(N, K, A))

Fixed submission:
MOD = 10 ** 9 + 7

def solve(N, K, A):
    A.sort()
    ans = 0
 
    for i in range(1, N):
        now = cmb(i, K - 1, MOD)
        ans += A[i] * now
 
    A.sort(reverse=True)
    for i in range(1, N):
        now = cmb(i, K - 1, MOD)
        ans += A[i] * (-now)
 
    return ans % MOD
 
 
# N = int(input())
# S = input()
N, K = map(int, input().split())
A = list(map(int, input().split()))

def cmb(n, r, p):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % p

p = 10 ** 9 + 7
fact = [1, 1]
factinv = [1, 1]
inv = [0, 1]
 
for i in range(2, N + 1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    factinv.append((factinv[-1] * inv[-1]) % p)


print(solve(N, K, A))

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

MOD = 10 ** 9 + 7


def comb(n, r):
    if (r < 0) or n < r:
        return 0
    return math.factorial(n) // (math.factorial(n - r) * math.factorial(r))


def solve(N, K, A):
    A.sort()
    ans = 0

    for i in range(1, N):
        now = comb(i, K - 1)
        ans += A[i] * now

    A.sort(reverse=True)
    for i in range(1, N):
        now = comb(i, K - 1)
        ans += A[i] * (-now)

    return ans % MOD


# N = int(input())
# S = input()
N, K = map(int, input().split())
A = list(map(int, input().split()))

print(solve(N, K, A))


Fixed submission:
MOD = 10 ** 9 + 7

def solve(N, K, A):
    A.sort()
    ans = 0
 
    for i in range(1, N):
        now = cmb(i, K - 1, MOD)
        ans += A[i] * now
 
    A.sort(reverse=True)
    for i in range(1, N):
        now = cmb(i, K - 1, MOD)
        ans += A[i] * (-now)
 
    return ans % MOD
 
 
# N = int(input())
# S = input()
N, K = map(int, input().split())
A = list(map(int, input().split()))

def cmb(n, r, p):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % p

p = 10 ** 9 + 7
fact = [1, 1]
factinv = [1, 1]
inv = [0, 1]
 
for i in range(2, N + 1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    factinv.append((factinv[-1] * inv[-1]) % p)


print(solve(N, K, A))