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.
            

Approach = Progression

Logic

After every 7 steps, we start from (start+1), where start=1

            1 2 3 4 5 6 7
            |
            start

            2 3 4 5 6 7 8
            |
            start+1
        

Code

                class Solution {
                    public:
                        int totalMoney(int n) {
                            int start = 1, j = start, i = 0, out = 0;
                            while (i < n) {
                                out += j;
                                j += 1;
                                i++;
                                if (i%7 == 0) {
                                    start += 1;
                                    j = start;
                                }
                            }
                            return out;
                        }
                    };
            

                class Solution {
                    public:
                        int totalMoney(int n) {
                            int start = 1, j = start, i = 0, out = 0;
                            /*
                            lambda expression
                            function_pointer  = [env var] (params) mutable throw -> return_type { 
                                .....function body ......
                            };
                            */
                            //CPP11 = lambda
                            //CPP14 = auto type deduction for the lambda
                            auto fun = [&]() {
                                out += j;
                                j += 1;
                                i++;
                                if (i%7 == 0) {
                                    start += 1;
                                    j = start;
                                }
                            };
                            while (i < n) {
                                fun();
                            }
                            return out;
                        }
                    };
            

                class Solution {
                    public:
                        int totalMoney(int n) {
                            int start = 1, j = start, i = 0, out = 0;
                    
                            //CPP17 = capture 3 values from lambda
                            auto updateCounters = [&]() -> std::tuple<int, int, int> {
                                out += j;
                                j += 1;
                                i++;
                                if (i % 7 == 0) {
                                    start += 1;
                                    j = start;
                                }
                                return std::make_tuple(out, j, i);
                            };
                    
                            while (i < n) {
                                std::tie(out, j, i) = updateCounters();
                            }
                    
                            return out;
                        }
                    };
            

                class Solution:
                def totalMoney(self, n: int) -> int:
                    start = 1
                    j = start
                    i = 0
                    out = 0
                    while i < n:
                        out += j
                        j += 1
                        i += 1
                        if i%7 == 0:
                            start += 1
                            j = start
                    return out
            

                impl Solution {
                    pub fn total_money(n: i32) -> i32 {
                        let mut start = 1;
                        let mut j = start;
                        let mut i = 0; 
                        let mut out = 0;
                        while (i < n) {
                            out += j;
                            j += 1;
                            i += 1;
                            if (i%7 == 0) {
                                start += 1;
                                j = start;
                            }
                        }
                        out
                    }
                }
            

                func totalMoney(n int) int {
                    start := 1
                    j := start 
                    i := 0
                    out := 0
                    for i < n {
                        out += j
                        j += 1
                        i++
                        if (i%7 == 0) {
                            start += 1
                            j = start
                        }
                    }
                    return out
                }