Algorithms: Implement Quick Sort

Algorithms/quicksort.js

@@ -0,0 +1,65 @@
+// 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]));