Description
Hercy wants to save money for his first car. He puts money in the Leetcode bank every day.
He starts by putting in $1 on Monday, the first day. Every day from Tuesday to Sunday, he will put in $1 more than the day before. On every subsequent Monday, he will put in $1 more than the previous Monday.
Given n, return the total amount of money he will have in the Leetcode bank at the end of the nth day.
Example 1:
Input: n = 4 Output: 10 Explanation: After the 4th day, the total is 1 + 2 + 3 + 4 = 10.
Example 2:
Input: n = 10 Output: 37 Explanation: After the 10th day, the total is (1 + 2 + 3 + 4 + 5 + 6 + 7) + (2 + 3 + 4) = 37. Notice that on the 2nd Monday, Hercy only puts in $2.
Example 3:
Input: n = 20 Output: 96 Explanation: After the 20th day, the total is (1 + 2 + 3 + 4 + 5 + 6 + 7) + (2 + 3 + 4 + 5 + 6 + 7 + 8) + (3 + 4 + 5 + 6 + 7 + 8) = 96.
Constraints:
1 <= n <= 1000
Solution
Python3
class Solution:
def totalMoney(self, n: int) -> int:
# Complete weeks sum = 28, 35, 52
# sum of AP = (n * [2a + (n – 1) * d]) / 2
completeWeeks = n // 7
remainingDays = n % 7
startMoney = completeWeeks + 1
completeWeeksSum = (completeWeeks * (2 * 28 + (completeWeeks - 1) * 7)) // 2
remSum = (remainingDays * (2 * startMoney + (remainingDays - 1))) // 2
return completeWeeksSum + remSum