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| 1 | +# Copyright (C) Deepali Srivastava - All Rights Reserved |
| 2 | +# This code is part of DSA course available on CourseGalaxy.com |
| 3 | + |
| 4 | +def merge_sort(a): |
| 5 | + n=len(a) |
| 6 | + temp = [None]*n |
| 7 | + size = 1 |
| 8 | + while size <= n-1: |
| 9 | + sort_pass(a, temp, size, n) |
| 10 | + size = size * 2 |
| 11 | + |
| 12 | +def sort_pass(a,temp,size,n): |
| 13 | + low1 = 0 |
| 14 | + while low1+size <= n-1: |
| 15 | + up1 = low1 + size - 1 |
| 16 | + low2 = low1 + size |
| 17 | + up2 = low2 + size - 1 |
| 18 | + |
| 19 | + if up2 >= n: # if length of last sublist is less than size |
| 20 | + up2 = n-1 |
| 21 | + |
| 22 | + merge(a, temp, low1, up1, low2, up2) |
| 23 | + |
| 24 | + low1 = up2 + 1 # Take next two sublists for merging |
| 25 | + |
| 26 | + for i in range(low1,n): |
| 27 | + temp[i] = a[i] # If any sublist is left alone |
| 28 | + |
| 29 | + copy(a, temp, n) |
| 30 | + |
| 31 | +# a[low1]...a[up1] and a[low2]...a[up2] merged to temp[low1]...temp[up2] */ |
| 32 | +def merge(a, temp, low1, up1, low2, up2): |
| 33 | + i = low1 |
| 34 | + j = low2 |
| 35 | + k = low1 |
| 36 | + |
| 37 | + while i <= up1 and j <= up2: |
| 38 | + if a[i] <= a[j]: |
| 39 | + temp[k] = a[i] |
| 40 | + i+=1 |
| 41 | + else: |
| 42 | + temp[k] = a[j] |
| 43 | + j+=1 |
| 44 | + k+=1 |
| 45 | + |
| 46 | + while i <= up1: |
| 47 | + temp[k] = a[i] |
| 48 | + i+=1 |
| 49 | + k+=1 |
| 50 | + |
| 51 | + while j <= up2: |
| 52 | + temp[k] = a[j] |
| 53 | + j+=1 |
| 54 | + k+=1 |
| 55 | + |
| 56 | +# copies temp[low]....temp[up] to a[low]...a[up] |
| 57 | +def copy(a, temp, n): |
| 58 | + for i in range(n): |
| 59 | + a[i] = temp[i] |
| 60 | + |
| 61 | + |
| 62 | +############################################################# |
| 63 | + |
| 64 | +list1 = [6,3,1,5,9,8] |
| 65 | +merge_sort(list1) |
| 66 | +print(list1) |
| 67 | + |
| 68 | +list2 = [2,3,5,39,11,8,9,166,45,23] |
| 69 | +merge_sort(list2) |
| 70 | +print(list2) |
| 71 | + |
| 72 | +list3 = [1,2,3,4,5,6,7,8,9,10] |
| 73 | +merge_sort(list3) |
| 74 | +print(list3) |
| 75 | + |
| 76 | +list4 = [10,9,8,7,6,5,4,3,2,1] |
| 77 | +merge_sort(list4) |
| 78 | +print(list4) |
| 79 | + |
| 80 | +list5 = [4] |
| 81 | +merge_sort(list5) |
| 82 | +print(list5) |
| 83 | + |
| 84 | +################################################################# |
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