Merge Sort Algorithm in python

projects/Merge_Sort_Algorithm/README.md

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+## Merge Sort Algorithm
+
+This script sorts the given array using merge sort algorithm. You can change the predefined "arr" to sort your array.
+
+### Prerequisites
+
+You only need python to run this script. You can visit [here](https://www.python.org/downloads/) to download python.
+
+### How to run the script
+
+Running the script is really simple! Just open a terminal in the folder where your script is located and run the following command :
+
+```
+python3 merge.py
+```
+
+### Sample use of the script
+
+```
+python3 merge.py
+
+  Given array is
+  100 50 80 20 70
+
+  Sorted array is
+  20 50 70 80 100
+
+```
+### Author Name
+
+Vrunda Jasani

projects/Merge_Sort_Algorithm/merge.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-l)//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 = [100, 50, 80, 25, 20, 5]
+n = len(arr)
+print("Given array is")
+for i in range(n):
+    print("%d" % arr[i],end=" ")
+
+mergeSort(arr, 0, n-1)
+print("\n\nSorted array is")
+for i in range(n):
+    print("%d" % arr[i],end=" ")