Create Merge_sort.py

Blooverh · Blooverh · commit df53141e1c57 · 2023-08-24T21:08:52.000-05:00
diff --git a/Sorting_algorithms/Merge_sort.py b/Sorting_algorithms/Merge_sort.py
@@ -0,0 +1,34 @@
+def merge(S1, S2, S):
+    """Merge 2 sorted python lists S1 and S2 into a properly sized list S"""
+
+    i=0
+    j=0
+
+    while i+j < len(S):
+        if j == len(S1) or (i < len(S1) and S1[i] < S2[j]):
+            S[i+j] = S1[i] # copy ith element of S1 as next item of S
+            i+=1
+        else:
+            S[i+j]= S2[j] # copy jth element of S2 as next item of S
+            j+=1
+
+def merge_sort(S):
+    """Sort the elements of S using the merge-sort algorithm"""
+
+    n= len(S)
+    if n < 2:
+        return 
+    
+    #divide
+    mid = n // 2
+    
+    S1 = S[0:mid] #copy first half
+    S2 = S[mid: n] #copy second half
+
+    #conquer
+    merge_sort(S1) # sort copy of first half
+    merge_sort(S2) # sort copy of second half
+
+    #merge results 
+
+    merge(S1, S2, S) #merge sorter halves back into S
