Pseudo Code

Lesson 4 of 9 in Coddy's Counting Sort - DSA Series course.

countingSort(array):
   max = largest value in array
   count = array of (max + 1) zeros
   for each x in array:          # count phase
      count[x] += 1
   result = []                   # rebuild phase
   for v from 0 to max:
      repeat count[v] times:
         append v to result
   return result

count[v] uses the value v as an index, so the value range decides the size of the count array.
The count phase tallies every value in one pass.
The rebuild phase emits each value the right number of times, in increasing order, producing a sorted array.

Try it yourself

This lesson doesn't include a code challenge.