Fixed merge sort, added quicksort

Author: nzakas

algorithms/sorting/merge-sort-iterative/merge-sort-iterative.js

@@ -55,12 +55,18 @@ function merge(left, right){
  * @return {Array} The sorted array.
  */
 function mergeSort(items){
-    if (items.length == 1) {
+
+    // Terminal condition - don't need to do anything for arrays with 0 or 1 items
+    if (items.length < 2) {
         return items;
     }
 
-    var work = [];
-    for (var i=0, len=items.length; i < len; i++){
+    var work = [],
+        i,
+        len;
+        
+        
+    for (i=0, len=items.length; i < len; i++){
         work.push([items[i]]);
     }
     work.push([]);  //in case of odd number of items

algorithms/sorting/merge-sort-recursive/merge-sort-inplace.js

@@ -0,0 +1,68 @@
+/*
+ * Recursive merge sort implementation in JavaScript
+ * Copyright (c) 2012 Nicholas C. Zakas
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+/**
+ * Merges to arrays in order based on their natural
+ * relationship.
+ * @param {Array} left The first array to merge.
+ * @param {Array} right The second array to merge.
+ * @return {Array} The merged array.
+ */
+function merge(left, right){
+    var result  = [],
+        il      = 0,
+        ir      = 0;
+
+    while (il < left.length && ir < right.length){
+        if (left[il] < right[ir]){
+            result.push(left[il++]);
+        } else {
+            result.push(right[ir++]);
+        }
+    }
+
+    return result.concat(left.slice(il)).concat(right.slice(ir));
+}
+
+/**
+ * Sorts an array in ascending natural order using
+ * merge sort.
+ * @param {Array} items The array to sort.
+ * @return {Array} The sorted array.
+ */
+function mergeSort(items){
+
+    if (items.length < 2) {
+        return items;
+    }
+
+    var middle = Math.floor(items.length / 2),
+        left    = items.slice(0, middle),
+        right   = items.slice(middle),
+        params = merge(mergeSort(left), mergeSort(right));
+    
+    // Add the arguments to replace everything between 0 and last item in the array
+    params.unshift(0, items.length);
+    items.splice.apply(items, params);
+    return items;
+}

algorithms/sorting/quicksort/quicksort.js

@@ -0,0 +1,104 @@
+/*
+ * Insertion sort implementation in JavaScript
+ * Copyright (c) 2012 Nicholas C. Zakas
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of items software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and items permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+/**
+ * Swaps two values in an array.
+ * @param {Array} items The array containing the items.
+ * @param {int} firstIndex Index of first item to swap.
+ * @param {int} secondIndex Index of second item to swap.
+ * @return {void}
+ */
+function swap(items, firstIndex, secondIndex){
+    var temp = items[firstIndex];
+    items[firstIndex] = items[secondIndex];
+    items[secondIndex] = temp;
+}
+
+function partition(items, left, right) {
+
+    var pivot   = items[Math.ceil((right + left) / 2)],  // pivot value is middle item
+        i       = left,     // starts from left and goes right to pivot index
+        j       = right;    // starts from right and goes left to pivot index
+
+
+    // while the two indices don't match
+    while (i <= j) {
+
+        // if the item on the left is less than the pivot, continue right
+        while (items[i] < pivot) {
+            i++;
+        }
+
+        // if the item on the right is greater than the pivot, continue left
+        while (items[j] > pivot) {
+            j--;
+        }
+
+        // if the two indices still don't match, swap the values
+        if (i <= j) {
+            swap(items, i, j);
+
+            // change indices to continue loop
+            i++;
+            j--;
+        }
+    }
+
+    // this value is necessary for recursion
+    return i;
+}
+
+/**
+ * A quicksort implementation in JavaScript. The array
+ * is sorted in place.
+ * @param {Array} items An array of items to sort.
+ * @return {Array} The sorted array.
+ */
+function quickSort(items, left, right) {
+
+    var index;
+
+    // performance - don't sort an array with zero or one items
+    if (items.length > 1) {
+
+        // fix left and right values - might not be provided
+        left = typeof left != "number" ? 0 : left;
+        right = typeof right != "number" ? items.length - 1 : right;
+
+        // split up the entire array
+        index = partition(items, left, right);
+
+        // if the returned index
+        if (left < index - 1) {
+            quickSort(items, left, index - 1);
+        }
+
+        if (index < right) {
+            quickSort(items, index + 1, right);
+        }
+
+    }
+
+    return items;
+}
+