heapCreation.js

//var arr = [7, 5, 1, 4, 2, 3,8]


function createHeap (arr) {
  var startIndex = Math.floor(arr.length / 2) - 1

  while(startIndex >= 0) {
    heapify(arr, startIndex)
    startIndex -= 1
  }
  return arr
}


function heapify (arr, startIndex) {
   var leftChild = arr[2 * startIndex + 1]
   var rightChild = arr[2 * startIndex + 2]
   var temp = arr[startIndex]

  // leaf node 
  if (!leftChild && !rightChild) {
    return
  }

  // right most node on n-1 level
  if (!rightChild) {
    if (leftChild < temp) {
      arr[startIndex] = leftChild
      arr[2 * startIndex + 1] = temp
    } 
    return
  }


   if (arr[startIndex] < leftChild && arr[startIndex] < rightChild) {
     return
   }

   var temp = arr[startIndex]
   if (leftChild < rightChild) {
     arr[startIndex] = leftChild
     arr[2 * startIndex + 1] = temp
     heapify(arr, 2 * startIndex + 1)
   } else {
     arr[startIndex] = rightChild
     arr[2 * startIndex + 2] = temp
     heapify(arr, 2 * startIndex + 2)
   }
}