做不对一点

import sys
MOD = 10**9 + 7

def solve():
n, k = map(int, sys.stdin.readline().split())
l = list(map(int, sys.stdin.readline().split()))
l.sort()

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


res = 0
left = 0
right = n - 1
while left <= right:
    if l[left] + l[right] >= k:
        res += right - left
        right -= 1
    else:
        left += 1


if res == 0:
    print(0)
else:
    ans = fact[n] * inv_fact[n - res] % MOD
    print(ans)

简单，太简单了