How to implement merge sort in JavaScript?

Javascript Object Oriented Programming Programming

Merge-Sort

Merge sort is an example of a divide-and-conquer type sorting-algorithm.The input of merge sort is an array of some elements, which are need to be arranged typically from least to the greatest.

Steps to follow in Merge Sort

Merge sort divides the array in to two sub arrays and later divides each array in to another two arrays and so on until a bunch of single element arrays are left. For instance, in the following example the array [4,7,5,9,1,3,8,2] divides in to single array elements such as [4], [7], [5], [9], [1], [3], [8], [2].
It starts comparing arrays in such a manner that two arrays are compared and concatenated. In the following example, it compares two arrays at a time that is [4], [7] are compared and concatenated then [5], [9] are compared and concatenated and so on such that arrays [4,7], [5,9], [1,3], [2,8] are formed.
It follows the same way that is two-two arrays are compared and concatenated to form two arrays. In the following example [4,7] and [5,9] are compared and concatenated to get an array as [4,5,7,9] and same is the case with other two arrays to form an array as [1,2,3,8].
Same rule applicable here that is the remaining two arrays compares and concatenates to get a final array as [1,2,3,4,5,7,8,9].

Example

Live Demo

<html>
<body>
<script>
   function mSort (array) {
      if (array.length === 1) {
      return array                            // return once we hit an array with a single item
   }
   const middle = Math.floor(array.length / 2) // get the middle item of the array rounded down
   const left = array.slice(0, middle)         // items on the left side
   const right = array.slice(middle)           // items on the right side
   document.write(middle);
   return merge(
      mSort(left),
      mSort(right)
   )
   }
   // compare the arrays item by item and return the concatenated result
   function merge (left, right) {
      let result = []
      let leftIndex = 0
      let rightIndex = 0
      while (leftIndex < left.length && rightIndex < right.length) {
         if (left[leftIndex] < right[rightIndex]) {
         result.push(left[leftIndex])
         leftIndex++
         document.write("</br>");        
         } else {
         result.push(right[rightIndex])
         rightIndex++      
      }
   }
   return result.concat(left.slice(leftIndex)).concat(right.slice(rightIndex))
   }
   const list = [4,7,5,9,1,3,8,2]
   document.write(mSort(list));
   </script>
   </body>
   </html>

Output

1,2,3,4,5,7,8,9

Vineeth.mariserla

Published on 31-May-2019 15:04:00

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