Added Merge Sort in Python

Sorting/Merge Sort/Python/Merge_sort.py

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+# Python program for implementation of MergeSort 
+
+# Merges two subarrays of arr[]. 
+# First subarray is arr[l..m] 
+# Second subarray is arr[m+1..r] 
+def merge(arr, l, m, r): 
+	n1 = m - l + 1
+	n2 = r- m 
+
+	# create temp arrays 
+	L = [0] * (n1) 
+	R = [0] * (n2) 
+
+	# Copy data to temp arrays L[] and R[] 
+	for i in range(0 , n1): 
+		L[i] = arr[l + i] 
+
+	for j in range(0 , n2): 
+		R[j] = arr[m + 1 + j] 
+
+	# Merge the temp arrays back into arr[l..r] 
+	i = 0	 # Initial index of first subarray 
+	j = 0	 # Initial index of second subarray 
+	k = l	 # Initial index of merged subarray 
+
+	while i < n1 and j < n2 : 
+		if L[i] <= R[j]: 
+			arr[k] = L[i] 
+			i += 1
+		else: 
+			arr[k] = R[j] 
+			j += 1
+		k += 1
+
+	# Copy the remaining elements of L[], if there 
+	# are any 
+	while i < n1: 
+		arr[k] = L[i] 
+		i += 1
+		k += 1
+
+	# Copy the remaining elements of R[], if there 
+	# are any 
+	while j < n2: 
+		arr[k] = R[j] 
+		j += 1
+		k += 1
+
+# l is for left index and r is right index of the 
+# sub-array of arr to be sorted 
+def mergeSort(arr,l,r): 
+	if l < r: 
+
+		# Same as (l+r)/2, but avoids overflow for 
+		# large l and h 
+		m = (l+(r-1))/2
+
+		# Sort first and second halves 
+		mergeSort(arr, l, m) 
+		mergeSort(arr, m+1, r) 
+		merge(arr, l, m, r) 
+
+
+# Driver code to test above 
+arr = [12, 11, 13, 5, 6, 7] 
+n = len(arr) 
+print ("Given array is") 
+for i in range(n): 
+	print ("%d" %arr[i]), 
+
+mergeSort(arr,0,n-1) 
+print ("\n\nSorted array is") 
+for i in range(n): 
+	print ("%d" %arr[i]), 
+
+# This code is contributed by Mohit Kumra 
+