Mergesort revised Jan 31 2017

Author: joeyajames

Mergesort.py

@@ -0,0 +1,30 @@
+# revised Mergesort. updated 1/31/2017 based on feedback from users.
+
+import sys
+	
+def merge_sort(A, first=0, last=len(A)-1):
+	if first < last:
+		middle = (first + last)//2
+		merge_sort(A, first, middle)
+		merge_sort(A, middle+1, last)
+		merge(A, first, middle, last)
+		
+def merge(A, first, middle, last):
+	L = A[first:middle+1]
+	R = A[middle+1:last+1]
+	L.append(sys.maxsize)
+	R.append(sys.maxsize)
+	i = j = 0
+	
+	for k in range (first, last+1):
+		if L[i] <= R[j]:
+			A[k] = L[i]
+			i += 1
+		else:
+			A[k] = R[j]
+			j += 1
+			
+A = [5,9,1,2,4,8,6,3,7]
+print(A)
+merge_sort(A)
+print(A)