add merge-sort (#264)

algorithms/JavaScript/README.md

@@ -15,6 +15,7 @@
 1. [Bubble Sort](src/sorting/bubble-sort.js)
 2. [Insertion Sort](src/sorting/insertion-sort.js)
 3. [Selection Sort](src/sorting/selection-sort.js)
+4. [Merge Sort](src/sorting/merge-sort.js)
  
 ## Strings
 1. [Palindrome](src/strings/palindrome.js)

algorithms/JavaScript/src/sorting/merge-sort.js

@@ -0,0 +1,32 @@
+function merge(left, right) {
+    let arr = []
+    // Break out of loop if any one of the array gets empty
+    while (left.length && right.length) {
+        // Pick the smaller among the smallest element of left and right sub arrays 
+        if (left[0] < right[0]) {
+            arr.push(left.shift())  
+        } else {
+            arr.push(right.shift()) 
+        }
+    }
+    
+    // Concatenating the leftover elements
+    // (in case we didn't go through the entire left or right array)
+    return [ ...arr, ...left, ...right ]
+}
+
+function mergeSort(array) {
+  const half = array.length / 2
+  
+  // Base case or terminating case
+  if(array.length < 2){
+    return array 
+  }
+  
+  const left = array.splice(0, half)
+  return merge(mergeSort(left),mergeSort(array))
+}
+
+//testing
+array = [4, 8, 7, 2, 11, 1, 3];
+console.log(mergeSort(array));