Buggy python submission (verdict: Time Limit Exceeded):
def cmb_mod_p(n, r, mod): # nCr mod p

    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)

    g1 = [1, 1]
    g2 = [1, 1]
    inverse = [0, 1]

    for i in range( 2, n + 1 ):
        g1.append( ( g1[-1] * i ) % mod )
        inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
        g2.append( (g2[-1] * inverse[-1]) % mod )

    return g1[n] * g2[r] * g2[n-r] % mod

n, k = map(int, input().split())
a = list( map(int, input().split()))
MOD = 10**9 + 7
ans = 0

a.sort()

for j in range(n):
    i = j +1
    if j <= n-k:
        minX = a[i-1]
        ans -= a[i-1]*cmb_mod_p(n-i,k-1,MOD)%MOD
    if k -1 <= i:
        maxX = a[i-1]
        ans += a[i-1]*cmb_mod_p(i-1,k-1,MOD)%MOD

print(ans%MOD)


Fixed submission:
def cmb(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return g1[n] * g2[r] * g2[n-r] % mod

mod = 10**9+7
N = 10**5
g1 = [1, 1]
g2 = [1, 1]
inverse = [0, 1]

for i in range( 2, N + 1 ):
    g1.append( ( g1[-1] * i ) % mod )
    inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2.append( (g2[-1] * inverse[-1]) % mod )

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

ans = 0


a.sort()

for j in range(n):
    i = j +1
    if j <= n-k:
        minX = a[i-1]
        ans -= a[i-1]*cmb(n-i,k-1,mod)%mod
    if k -1 <= i:
        maxX = a[i-1]
        ans += a[i-1]*cmb(i-1,k-1,mod)%mod

print(ans%mod)

Buggy python submission (verdict: Runtime Error):
def cmb(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return g1[n] * g2[r] * g2[n-r] % mod

mod = 10**9+7
N = 10**4
g1 = [1, 1]
g2 = [1, 1]
inverse = [0, 1]

for i in range( 2, N + 1 ):
    g1.append( ( g1[-1] * i ) % mod )
    inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2.append( (g2[-1] * inverse[-1]) % mod )

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

ans = 0


a.sort()

print(a)

for j in range(n):
    i = j +1
    if j <= n-k:
        minX = a[i-1]
        ans -= a[i-1]*cmb(n-i,k-1,mod)%mod
    if k -1 <= i:
        maxX = a[i-1]
        ans += a[i-1]*cmb(i-1,k-1,mod)%mod

print(ans%mod)




Fixed submission:
def cmb(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return g1[n] * g2[r] * g2[n-r] % mod

mod = 10**9+7
N = 10**5
g1 = [1, 1]
g2 = [1, 1]
inverse = [0, 1]

for i in range( 2, N + 1 ):
    g1.append( ( g1[-1] * i ) % mod )
    inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2.append( (g2[-1] * inverse[-1]) % mod )

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

ans = 0


a.sort()

for j in range(n):
    i = j +1
    if j <= n-k:
        minX = a[i-1]
        ans -= a[i-1]*cmb(n-i,k-1,mod)%mod
    if k -1 <= i:
        maxX = a[i-1]
        ans += a[i-1]*cmb(i-1,k-1,mod)%mod

print(ans%mod)

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

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

ans = 0

MOD = 10**9 + 7

for v in itertools.combinations(a, k):
    ans += (max(v) - min(v))%MOD

print(ans%MOD)


Fixed submission:
def cmb(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return g1[n] * g2[r] * g2[n-r] % mod

mod = 10**9+7
N = 10**5
g1 = [1, 1]
g2 = [1, 1]
inverse = [0, 1]

for i in range( 2, N + 1 ):
    g1.append( ( g1[-1] * i ) % mod )
    inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2.append( (g2[-1] * inverse[-1]) % mod )

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

ans = 0


a.sort()

for j in range(n):
    i = j +1
    if j <= n-k:
        minX = a[i-1]
        ans -= a[i-1]*cmb(n-i,k-1,mod)%mod
    if k -1 <= i:
        maxX = a[i-1]
        ans += a[i-1]*cmb(i-1,k-1,mod)%mod

print(ans%mod)