freeCodeCamp/Algorithms/quicksort.js

// https://www.freecodecamp.org/learn/coding-interview-prep/algorithms/implement-quick-sort

function quickSort(array) {
  // Only change code below this line
  const swap = (array, indexA, indexB) => {
    const temp = array[indexA];
    array[indexA] = array[indexB];
    array[indexB] = temp;
  };

  const medianIndex = (array, indexA, indexB, indexC) => {
    const lowerIndex = array[indexA] < array[indexB] ? indexA : indexB;
    const higherIndex = array[lowerIndex] > array[indexC] ? lowerIndex : indexC;
    const pivotIndex =
      array[indexA] < array[higherIndex] ? indexA : higherIndex;
    return pivotIndex;
  };

  const partition = (array, startIndex, endIndex) => {
    const midIndex = Math.floor(startIndex + (endIndex - startIndex) / 2);
    const pivotIndex = medianIndex(array, startIndex, midIndex, endIndex);
    const pivot = array[pivotIndex];
    swap(array, pivotIndex, endIndex);
    let lowIndex = startIndex;
    let highIndex = endIndex - 1;
    while (lowIndex < highIndex) {
      for (; lowIndex < highIndex; lowIndex++) {
        if (array[lowIndex] > pivot) break;
      }
      for (; highIndex >= lowIndex; highIndex--) {
        if (array[highIndex] < pivot) break;
      }
      if (lowIndex < highIndex) swap(array, lowIndex, highIndex);
    }
    if (array[lowIndex] > array[endIndex]) {
      swap(array, lowIndex, endIndex);
      return lowIndex;
    }
    return endIndex;
  };

  // To-do: make it non-recursive
  const quicksort_ = (array, startIndex, endIndex) => {
    if (startIndex < endIndex) {
      const pivotIndex = partition(array, startIndex, endIndex);
      if (pivotIndex - 1 > startIndex)
        quicksort_(array, startIndex, pivotIndex - 1);
      if (pivotIndex + 1 < endIndex)
        quicksort_(array, pivotIndex + 1, endIndex);
    }
  };

  quicksort_(array, 0, array.length - 1);

  return array;
  // Only change code above this line
}

console.log(
  quickSort([
    1, 4, 2, 8, 345, 123, 43, 32, 5643, 63, 123, 43, 2, 55, 1, 234, 92,
  ])
);

console.log(quickSort([2, 6, 5, 3, 8, 7, 1, 0]));