count_valid_pickup_delivery.py (693B)
| # 1359. Count All Valid Pickup and Delivery Options
"""
given 'n' orders, each order consists in pickup and delivery services. count
all valid pickup/delivery possible sequences such that 'delivery[i]' is
always after 'pickup[i]'. since the answer may be too large, return it modulo
10^9+7
"""
class Solution(object):
def countOrders(self, n):
dp = [0] * (n + 1)
dp[1] = 1
for i in range(2, n + 1):
dp[i] = (i * dp[i - 1] * (2 * i - 1)) % (10**9 + 7)
return dp[n]
if __name__ == "__main__":
obj = Solution
print(obj.countOrders(1)) # expect: 1
print(obj.countOrders(2)) # expect: 6
print(obj.countOrders(3)) # expect: 90
|
