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 $n^{\text{th}}$ 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:
$1 \leq n \leq 1000$
Refer to the hand-writing picture below.
- Tuesday, 16 March, 2021
- Time Complexity:
$O(1)$ - Space Complexity:
$O(1)$ - Runtime: 0 ms, faster than 100.00% of C online submissions for Calculate Money in Leetcode Bank.
- Memory Usage: 5.5 MB, less than 55.63% of C online submissions for Calculate Money in Leetcode Bank.
int totalMoney(int n) {
// w is the number of full-week past.
int w = n / 7;
// r is the number of days which could not be calculated as a full week.
int r = n % 7;
// Careful! Because of the integer data type, 49/2 is equal to 24 rather
// than 24.5, so we need to multiple it by 2 and then divided it by 2.
return (2 * w * r + r * r + r + 7 * w * w + 49 * w) / 2;
}