TheAlgorithms · itsvinayak · Aug 19, 2020 · Aug 17, 2020 · Aug 17, 2020
@@ -102,6 +102,7 @@
   * [HeapSort](https://github.com/TheAlgorithms/Javascript/blob/master/Sorts/HeapSort.js)
   * [HeapSortV2](https://github.com/TheAlgorithms/Javascript/blob/master/Sorts/HeapSortV2.js)
   * [InsertionSort](https://github.com/TheAlgorithms/Javascript/blob/master/Sorts/InsertionSort.js)
+  * [IntroSort](https://github.com/TheAlgorithms/Javascript/blob/master/Sorts/IntroSort.js)
   * [MergeSort](https://github.com/TheAlgorithms/Javascript/blob/master/Sorts/MergeSort.js)
   * [QuickSort](https://github.com/TheAlgorithms/Javascript/blob/master/Sorts/QuickSort.js)
   * [RadixSort](https://github.com/TheAlgorithms/Javascript/blob/master/Sorts/RadixSort.js)

@@ -0,0 +1,307 @@
+/**
+ * @function Intosort (As implemented in STD C++ Lib)
+ * The function performs introsort which is used in
+ * C++ Standard LIbrary, the implemntation is inspired from]
+ * library routine itself.
+ * ALGORITHM:
+ * 1) It performs quicksort on array until the recursion depth
+ *    exceeds a pre determined limit.
+ * 2) If the limit is reached it switches to heapsort
+ * 3) For array size less than a threshold(16) directly
+ *    does insertion sort on array
+ * @param {Array} array the array to be sorted
+ * @param {Function} compare the comparison function
+ *
+ * @see [Introsort](https://en.wikipedia.org/wiki/Introsort)
+ * @author [Lakhan Nad](https://github.com/Lakhan-Nad)
+ */
+function introsort (array, compare) {
+  /**
+   * @function Default Comparison Function
+   * This function is same as implemented by
+   * Array.sort method
+   * @see [StackOverflow](https://stackoverflow.com/questions/47334234/how-to-implement-array-prototype-sort-default-compare-function)
+   * @param {*} a variable 1
+   * @param {*} b variable 2
+   * @returns {Number}
+   * -1 if a is less than b
+   *  0 if a is equal to b
+   *  1 if a greater than b
+   */
+  var defaultComparator = function (x, y) {
+    if (x === undefined && y === undefined) return 0
+    if (x === undefined) return 1
+    if (y === undefined) return -1
+    var xString = toString(x)
+    var yString = toString(y)
+    if (xString < yString) return -1
+    if (xString > yString) return 1
+    return 0
+  }
+  /**
+   * @function helper function for defaultComparator
+   * Converts a given object to String
+   * @throws TypeError()
+   * @param {Object} obj
+   * @returns {String} String representation of given object
+   */
+  var toString = function (obj) {
+    if (obj === null) return 'null'
+    if (typeof obj === 'boolean' || typeof obj === 'number') {
+      return obj.toString()
+    }
+    if (typeof obj === 'string') return obj
+    if (typeof obj === 'symbol') throw new TypeError()
+    return obj.toString()
+  }
+  /**
+   * Checks if the value passed is an array
+   * or not
+   */
+  if (Array.isArray(array) === false) {
+    return
+  }
+  /**
+   * If the compare parameter is not a function
+   * or not passed at all use default comparator
+   * function
+   */
+  if (typeof compare !== 'function') {
+    compare = defaultComparator // If compare is not a comparator function
+  }
+  /**
+   * Use a closure to define the whole sort
+   * implementation this is done through
+   * [IIFE](https://en.wikipedia.org/wiki/Immediately_invoked_function_expression)
+   */
+  return (function (array, comparator) {
+    var swap = function (index1, index2) {
+      var temp = array[index1]
+      array[index1] = array[index2]
+      array[index2] = temp
+    }
+    /**
+     * @constant THRESHOLD
+     * If the length of array is less than
+     * this then we simply perform insertion sort
+     */
+    var THRESHOLD = 16
+    /**
+     * @constant TUNEMAXDEPTH
+     * Constant usec to increase or decrease value
+     * of maxDepth
+     */
+    var TUNEMAXDEPTH = 1
+    var len = array.length
+    /**
+     * Return if array is only of length 1
+     * Array of size 1 is always sorted
+     */
+    if (len === 1) {
+      return
+    }
+    /**
+     * Calculate maxDepth = log2(len)
+     * Taken from implementation in stdc++
+     */
+    var maxDepth = Math.floor(Math.log2(len)) * TUNEMAXDEPTH
+    /**
+     * The very first call to quicksort
+     * this initiates sort routine
+     */
+    quickSort(0, len, maxDepth)
+    /**
+     * A final checlk call to insertion sort
+     * on sorted array
+     */
+    insertionSort(0, len)
+    /** *********************  Implementation of various routines  **************************/
+    /**
+     * @function
+     * This is recursive quicksort implementation in array
+     * of segment [start,last-1]
+     * [QuickSort](https://en.wikipedia.org/wiki/Quicksort)
+     * @param {Number} start the start index of array segment to be sorted
+     * @param {Number} last  one more than the last index of array segment
+     * @param {Number} depth this measures how many recursive calls are done
+     */
+    function quickSort (start, last, depth) {
+      if (last - start <= THRESHOLD) {
+        insertionSort(start, last)
+        return
+      } else if (depth <= 0) {
+        heapSort(start, last)
+        return
+      }
+      var pivot = (last + start) >> 1
+      pivot = partition(start, last, pivot)
+      quickSort(start, pivot, depth - 1)
+      quickSort(pivot + 1, last, depth - 1)
+    }
+    /**
+     * @function Helper function to quicksort
+     * @param {Number} start the start of array segment to partitiion
+     * @param {Number} last  one more than last index of the array segment
+     * @param {Number} pivot the index of pivot to be used
+     * @returns {Number} the index of pivot after partition
+     */
+    function partition (start, last, pivot) {
+      swap(start, pivot)
+      pivot = start
+      var lo = start
+      var hi = last
+      while (true) {
+        lo++
+        while (comparator(array[lo], array[pivot]) <= 0 && lo !== last) {
+          lo++
+        }
+        hi--
+        while (comparator(array[hi], array[pivot]) > 0 && hi !== start) {
+          hi--
+        }
+        if (lo >= hi) {
+          break
+        }
+        swap(lo, hi)
+      }
+      swap(start, hi)
+      return hi
+    }
+    /**
+     * @function
+     * Performs insertion sort on array of range
+     * [start, last-1]
+     * @param {Number} start the first index of array segment to be sorted
+     * @param {Number} last  one more than last index of array to be sorted
+     */
+    function insertionSort (start, last) {
+      var i, j
+      for (i = start + 1; i < last; i++) {
+        j = i - 1
+        while (j >= 0 && comparator(array[j], array[j + 1]) > 0) {
+          swap(j, j + 1)
+          j--
+        }
+      }
+    }
+    /**
+     * @function
+     * Performs heapsort in array segment of range [start, last-1]
+     * [HeapSort](https://en.wikipedia.org/wiki/Heapsort)
+     * @param {Number} start the first index of array segment to be sorted
+     * @param {Number} last  one more than last index of array to be sorted
+     */
+    function heapSort (start, last) {
+      var x = (last + start) >> 1
+      while (x - start >= 0) {
+        heapify(x, start, last)
+        x--
+      }
+      x = last - 1
+      while (x - start > 0) {
+        swap(start, x)
+        heapify(start, start, x)
+        x--
+      }
+    }
+    /**
+     * @function Helper function to heapsort routine
+     * @param {Number} cur the index we need to heapify
+     * @param {Number} start the start index of array segment that cur belongs to
+     * @param {Number} last  one more than last index of segment that cur belongs to
+     */
+    function heapify (cur, start, last) {
+      var size = last - start
+      var max, lt, rt
+      cur = cur - start
+      while (true) {
+        max = cur
+        lt = 2 * max + 1
+        rt = 2 * max + 2
+        if (
+          lt < size &&
+          comparator(array[start + max], array[start + lt]) < 0
+        ) {
+          max = lt
+        }
+        if (
+          rt < size &&
+          comparator(array[start + max], array[start + rt]) < 0
+        ) {
+          max = rt
+        }
+        if (max !== cur) {
+          swap(start + cur, start + max)
+          cur = max
+        } else {
+          break
+        }
+      }
+    }
+  })(array, compare)
+}
+
+/**
+ * @example Demo run of the sort routine
+ * The data is randomly generated
+ * Prints RIGHT:) if the sort routine worked as expected
+ * If not prints WRONG!!
+ */
+(function demo () {
+  const data = []
+  const size = 1000000
+  var i = 0
+  var temp
+  var c = function (a, b) {
+    return a - b
+  }
+  for (i = 0; i < size; i++) {
+    temp = Math.random() * Number.MAX_SAFE_INTEGER
+    data.push(temp)
+  }
+  introsort(data, c)
+  var faulty = false
+  for (i = 1; i < size; i++) {
+    if (data[i] < data[i - 1]) {
+      faulty = true
+      break
+    }
+  }
+  if (faulty) {
+    console.log('WRONG!!')
+  } else {
+    console.log('RIGHT:)')
+  }
+})();
+
+/**
+ * @example Demo run of the sort routine
+ * using the default compare function and
+ * comparing the results with Array.sort
+ */
+(function demo () {
+  const data = []
+  const data2 = []
+  const size = 1000000
+  var i = 0
+  var temp
+  for (i = 0; i < size; i++) {
+    temp = Math.random() * Number.MAX_SAFE_INTEGER
+    data.push(temp)
+    data2.push(temp)
+  }
+  introsort(data)
+  data2.sort()
+  var faulty = false
+  for (i = 1; i < size; i++) {
+    if (data[i] !== data2[i]) {
+      faulty = true
+      break
+    }
+  }
+  if (faulty) {
+    console.log('WRONG Implented Comparator!!')
+  } else {
+    console.log('Comparator Works Fine:)')
+  }
+})()