Implementation of Heap sort

[theasteve]

AlgorithmsSedgewick/2-Sorting/2-4-PriorityQueues/Heap.java

Line 58 in 06703c1

private static void exch(Object[] pq, int i, int j) {

Thanks for your work on this. I'm currently going over the book and I have been a little off by the section on Heapsort. One of the things that I was confused about was dealing with the index 1 to N in the sorting method. I noticed from your implementation that you use -1 in the swap and in the less but have you tested?

class Heap
  # Trickledown
  def sink(a, k, n)
    while 2 * k <= n
      j = 2 * k # child

      if !a[j + 1].nil? # check if there is a right child
        j += 1 if j > 1 && less(a, j, j + 1) # if left child less than right child
      end

      break if !less(a, k, j) # If parent greater than child break

      swap(a, k, j)
      k = j
    end
  end

  def sort(a)
    n = a.length
    k = n / 2

    while k >= 1
      sink(a, k, n)
      k -= 1
    end

    while n > 1
      swap(a, 1, n)
      n -= 1
      sink(a, 1, n)
    end
    a
  end

  def less(pq, i, j)
    pq[i - 1] < pq[j - 1]
  end

  def swap(a, i, j)
    temp = a[i - 1]
    a[i - 1] = a[j - 1]
    a[j - 1] = temp
  end
end

When I do your implementation in Ruby I get the error for as the answer ["A", "M", "E", "L", "E", "O", "P", "R", "S", "T", "X"] and I haven't been able to figure out why.

I created the following post on Stackoverflow
https://stackoverflow.com/questions/63634906/ruby-heapsort-sink-undefined-method-for-nilnilclass

trying to figure out where am I off.