count_the_digit.js

//Count the Digit
//Level: 7kyu
/*
Take an integer n (n >= 0) and a digit d (0 <= d <= 9) as an integer. Square all numbers k (0 <= k <= n) between 0 
and n. Count the numbers of digits d used in the writing of all the k**2. Call nb_dig (or nbDig or ...) the function
taking n and d as parameters and returning this count.

Examples:

n = 10, d = 1, the k*k are 0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100
We are using the digit 1 in 1, 16, 81, 100. The total count is then 4.

nb_dig(25, 1):
1, 4, 9, 10, 11, 12, 13, 14, 19, 21 squared are 1, 16, 81, 100, 121, 144, 169, 196, 361, 441
so there are 11 digits `1` for the squares of numbers between 0 and 25.
Note that 121 has twice the digit 1.
*/

function nbDig(n, d) 
{
   var str_d=d.toString();
   var count=0;
   while(n>=0)
   {
       var num=(n*n).toString();
       var matchesCount = num.split(str_d).length - 1;
       count+=matchesCount;
       n--;
   }
   return count;
}