radixSort.swift

/*

  Sorting Algorithm that sorts an input array of integers digit by digit.

*/

// NOTE: This implementation does not handle negative numbers
func radixSort(_ array: inout [Int] ) {
  let radix = 10  //Here we define our radix to be 10
  var done = false
  var index: Int
  var digit = 1  //Which digit are we on?

  while !done {  //While our  sorting is not completed
    done = true  //Assume it is done for now

    var buckets: [[Int]] = []  //Our sorting subroutine is bucket sort, so let us predefine our buckets

    for _ in 1...radix {
      buckets.append([])
    }

    for number in array {
      index = number / digit  //Which bucket will we access?
      buckets[index % radix].append(number)
      if done && index > 0 {  //If we arent done, continue to finish, otherwise we are done
        done = false
      }
    }

    var i = 0

    for j in 0..<radix {
      let bucket = buckets[j]
      for number in bucket {
        array[i] = number
        i += 1
      }
    }

    digit *= radix  //Move to the next digit
  }
}