Problem
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
/**
* @param {number} n
* @return {number}
*/
var totalMoney = function(n) {
var weeks = Math.floor(n / 7);
var lastWeekDays = n % 7;
var sumOfWeeks = (4 + 4 + weeks - 1) * 7 * weeks / 2;
var sumOfLastDays = Array(lastWeekDays).fill(0).reduce((sum, _, i) => {
return sum + (i + 1) + weeks;
}, 0);
return sumOfWeeks + sumOfLastDays;
};
Explain:
nope.
Complexity:
- Time complexity : O(1).
- Space complexity : O(1).