25_Calculate_Money_in_Leetcode_Bank.cpp

// 1716. Calculate Money in Leetcode Bank

// 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

class Solution
{
public:
    int triSum(int n)
    {
        return (n * (n + 1)) >> 1;
    }

    int totalMoney(int days)
    {
        int nWeeks = days / 7;
        int rDays = days % 7;

        return triSum(days) - 42 * triSum(nWeeks - 1) - 6 * nWeeks * rDays;
    }
};