financeOnAnotherPlanet.js

// I need to save some money to buy a gift. I think I can do 
// something like that:

// First week (W0) I save nothing on Sunday, 1 on Monday, 2 on 
// Tuesday... 6 on Saturday, second week (W1) 2 on Monday... 7 
// on Saturday and so on according to the table below where the 
// days are numbered from 0 to 6.

// Can you tell me how much I will have for my gift on Saturday 
// evening after I have saved 12? (Your function finance(6) 
//   should return 168 which is the sum of the savings in the table).

// Imagine now that we live on planet XY140Z-n where the days of 
// the week are numbered from 0 to n (integer n > 0) and where I 
// save from week number 0 to week number n included (in the 
//   table below n = 6).

// How much money would I have at the end of my financing plan 
// on planet XY140Z-n?

// --  Su  Mo  Tu  We  Th  Fr  Sa
// W6                          12  
// W5                      10  11  
// W4                  8   9   10    
// W3              6   7   8   9   
// W2          4   5   6   7   8   
// W1      2   3   4   5   6   7   
// W0  0   1   2   3   4   5   6   

// Example:

// finance(5) --> 105
// finance(6) --> 168
// finance(7) --> 252
// finance(5000) --> 62537505000
// Hint:

// try to avoid nested loops!


function finance(n) {
    var total = 0;
    var start = 0;
    var end = n + 1;
    while (start !== end) {
      for (var i = start; i < end; i++) {
        total += i;
      }
      start += 2;
      end++;
    }
    return total;
}