Adding Merge and Quick Sort

Author: Vishal-raj-1

Sorting/README.md

@@ -6,6 +6,12 @@
   </a>
 </p>
 
+<p align="center">
+  <a href="https://youtu.be/4n90F6PCQ6A">
+  <img src="https://img.youtube.com/vi/4n90F6PCQ6A/0.jpg" alt="Sorting In JavaScript" />
+  </a>
+</p>
+
 ### Sort an Array
 ```javascript
 const arr = [-2, -7, 1000, 5]
@@ -76,4 +82,127 @@ const insertionSort = (arr) => {
 }
 
 console.log(insertionSort(arr)) // -7, -2 , 5, 1000
-```
+```
+
+### Merge Sort in JavaScript 
+```javascript
+const mergeSort = (arr) => {
+    if (arr.length < 2) {
+        return arr;
+    }
+    let mid = Math.floor(arr.length / 2);
+    let left = mergeSort(arr.slice(0, mid))
+    let right = mergeSort(arr.slice(mid))
+    return merge(left, right)
+}
+
+const merge = (left, right) => {
+    const result = []
+    let leftIndex = 0, rightIndex = 0;
+    while (leftIndex < left.length && rightIndex < right.length) {
+        if (left[leftIndex] < right[rightIndex]) {
+            result.push(left[leftIndex])
+            leftIndex++;
+        }
+        else {
+            result.push(right[rightIndex])
+            rightIndex++;
+        }
+    }
+
+    while (leftIndex < left.length) {
+        result.push(left[leftIndex])
+        leftIndex++;
+    }
+
+    while (rightIndex < right.length) {
+        result.push(right[rightIndex])
+        rightIndex++;
+    }
+
+    return result;
+}
+
+const arr1 = [29, 10, 8, 16, 37, 14, 4, 45]
+console.log(mergeSort(arr1))
+```
+### Merge Sort in JavaScript (Space Optimised)
+
+```javascript
+const mergeSortInplace = (arr, low, high) => {
+    if (low < high) {
+        let mid = Math.floor((low + high) / 2);
+        mergeSortInplace(arr, low, mid)
+        mergeSortInplace(arr, mid + 1, high)
+        mergeInplace(arr, low, mid, high)
+    }
+}
+
+const mergeInplace = (arr, low, mid, high) => {
+    const result = []
+    let leftIndex = low, rightIndex = mid + 1;
+    while (leftIndex <= mid && rightIndex <= high) {
+        if (arr[leftIndex] < arr[rightIndex]) {
+            result.push(arr[leftIndex])
+            leftIndex++;
+        }
+        else {
+            result.push(arr[rightIndex])
+            rightIndex++;
+        }
+    }
+
+    while (leftIndex <= mid) {
+        result.push(arr[leftIndex])
+        leftIndex++;
+    }
+
+    while (rightIndex <= high) {
+        result.push(arr[rightIndex])
+        rightIndex++;
+    }
+
+    for (let i = low; i <= high; i++) {
+        arr[i] = result[i - low];
+    }
+}
+
+const arr1 = [29, 10, 8, 16, 37, 14, 4, 45]
+console.log(mergeSortInplace(arr1, 0, arr.length - 1))
+console.log(arr1)
+```
+
+### Quick Sort in JavaScript
+
+```javascript
+const quickSort = (arr) => {
+    if(arr.length < 2){
+        return arr;
+    }
+    let pivotIndex = Math.floor(Math.random() * arr.length);
+    let left = [], right = [];
+    for(let i=0; i<arr.length; i++){
+        if(i === pivotIndex)
+            continue;
+
+        if(arr[i] < arr[pivotIndex]){
+            left.push(arr[i])
+        }
+        else{
+            right.push(arr[i])
+        }
+    }
+
+    return [...quickSort(left), arr[pivotIndex], ...quickSort(right)]
+}
+
+console.log(quickSort(arr1))
+```
+
+## Practice Question
+
+- [How Many Numbers are smaller than the current number](https://leetcode.com/problems/how-many-numbers-are-smaller-than-the-current-number)
+- [Merge Sorted Array](https://leetcode.com/problems/merge-sorted-array)
+- [Sort an Array](https://leetcode.com/problems/sort-an-array)
+- [Largest Number](https://leetcode.com/problems/largest-number)
+- [Sort Color](https://leetcode.com/problems/sort-colors)