Quicksort

Partition(numbers, lowIndex, highIndex) {
   // Pick middle element as pivot
   midpoint = lowIndex + (highIndex - lowIndex) / 2
   pivot = numbers[midpoint]
   
   done = false
   while (!done) {
      // Increment lowIndex while numbers[lowIndex] < pivot
      while (numbers[lowIndex] < pivot) {
         lowIndex += 1
      }
      
      // Decrement highIndex while pivot < numbers[highIndex]
      while (pivot < numbers[highIndex]) {
         highIndex -= 1
      }
      
      // If zero or one elements remain, then all numbers are 
      // partitioned. Return highIndex.
      if (lowIndex >= highIndex) {
         done = true
      }
      else {
         // Swap numbers[lowIndex] and numbers[highIndex]
         temp = numbers[lowIndex]
         numbers[lowIndex] = numbers[highIndex]
         numbers[highIndex] = temp
         
         // Update lowIndex and highIndex
         lowIndex += 1
         highIndex -= 1
      }
   }
   
   return highIndex
}

Quicksort(numbers, lowIndex, highIndex) {
   // Base case: If the partition size is 1 or zero 
   // elements, then the partition is already sorted
   if (lowIndex >= highIndex) {
      return
   }
   
   // Partition the data within the array. Value lowEndIndex 
   // returned from partitioning is the index of the low 
   // partition's last element.
   lowEndIndex = Partition(numbers, lowIndex, highIndex)
   
   // Recursively sort low partition (lowIndex to lowEndIndex) 
   // and high partition (lowEndIndex + 1 to highIndex)
   Quicksort(numbers, lowIndex, lowEndIndex)
   Quicksort(numbers, lowEndIndex + 1, highIndex)
}