added marge sort in py

Algorithms/Algorithms/Marge sort/marge sort.py

@@ -0,0 +1,49 @@
+# iterative way
+def mergeSort(a):
+   current_size = 1
+   # traversing subarrays
+   while current_size < len(a) - 1:
+      left = 0
+      # subarray being sorted
+      while left < len(a)-1:
+         # calculating mid value
+         mid = left + current_size - 1
+         # current_size
+         right = ((2 * current_size + left - 1, len(a) - 1)[2 * current_size + left - 1 > len(a)-1])
+         # Merge
+         merge(a, left, mid, right)
+         left = left + current_size*2
+      # Increasing sub array size
+      current_size = 2 * current_size
+# Merge
+def merge(a, l, m, r):
+   n1 = m - l + 1
+   n2 = r - m
+   L = [0] * n1
+   R = [0] * n2
+   for i in range(0, n1):
+      L[i] = a[l + i]
+   for i in range(0, n2):
+      R[i] = a[m + i + 1] i, j, k = 0, 0, l
+   while i < n1 and j < n2:
+      if L[i] > R[j]:
+         a[k] = R[j]
+         j += 1
+      else:
+         a[k] = L[i]
+         i += 1
+      k += 1
+   while i < n1:
+      a[k] = L[i]
+      i += 1
+      k += 1
+   while j < n2:
+      a[k] = R[j]
+      j += 1
+      k += 1
+# Driver code
+a = [2,5,3,8,6,5,4,7]
+mergeSort(a)
+print("Sorted array is:")
+for i in range(len(a)):
+   print (a[i],end=" ")