Improve python version of merge sort. (#23005)

guide/english/algorithms/sorting-algorithms/merge-sort/index.md

@@ -211,46 +211,37 @@ void mergesort(int A[],int size_a,int B[],int size_b,int C[])
 ### Implementation in Python
 
 ```python
-temp = None
-def merge(arr, left, right):
-    global temp, inversions
-    mid = (left + right) // 2
-    for i in range(left, right + 1):
-        temp[i] = arr[i]
-    
-    k, L, R = left, left, mid + 1
-    while L <= mid and R <= right:
-        if temp[L] <= temp[R]:
-            arr[k] = temp[L]
-            L += 1
-        else:
-            arr[k] = temp[R]
-            R += 1
-        k += 1
-    
-    while L <= mid:
-        arr[k] = temp[L]
-        L += 1
-        k += 1
-        
-    while R <= right:
-        arr[k] = temp[R]
-        R += 1
-        k += 1    
-        
-def merge_sort(arr, left, right):
-    if left >= right:
-        return
-    
-    mid = (left + right) // 2
-    merge_sort(arr, left, mid)
-    merge_sort(arr, mid + 1, right)
-    merge(arr, left, right)
+def merge(left,right,compare):
+	result = [] 
+	i,j = 0,0
+	while (i < len(left) and j < len(right)):
+		if compare(left[i],right[j]):
+			result.append(left[i])
+			i += 1
+		else:
+			result.append(right[j])
+			j += 1
+	while (i < len(left)):
+		result.append(left[i])
+		i += 1
+	while (j < len(right)):
+		result.append(right[j])
+		j += 1
+	return result
 
-arr = [1,6,3,1,8,4,2,9,3]
-temp = [None for _ in range(len(arr))]
-merge_sort(arr, 0, len(arr) - 1)
-print(arr, inversions)
+def merge_sort(arr, compare = lambda x, y: x < y):
+     #Used lambda function to sort array in both(increasing and decresing) order.
+     #By default it sorts array in increasing order
+	if len(arr) < 2:
+		return arr[:]
+	else:
+		middle = len(arr) // 2
+		left = merge_sort(arr[:middle], compare)
+		right = merge_sort(arr[middle:], compare)
+		return merge(left, right, compare) 
+
+arr = [2,1,4,5,3]
+print(merge_sort(arr))
 ```
 
 ### Implementation in Java