79 lines
1.7 KiB
Python
79 lines
1.7 KiB
Python
# Python program for implementation of MergeSort
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# Merges two subarrays of arr[].
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# First subarray is arr[l..m]
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# Second subarray is arr[m+1..r]
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def merge(arr, l, m, r):
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n1 = m - l + 1
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n2 = r - m
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# create temp arrays
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L = [0] * (n1)
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R = [0] * (n2)
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# Copy data to temp arrays L[] and R[]
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for i in range(0, n1):
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L[i] = arr[l + i]
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for j in range(0, n2):
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R[j] = arr[m + 1 + j]
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# Merge the temp arrays back into arr[l..r]
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i = 0 # Initial index of first subarray
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j = 0 # Initial index of second subarray
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k = l # Initial index of merged subarray
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while i < n1 and j < n2:
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if L[i] <= R[j]:
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arr[k] = L[i]
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i += 1
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else:
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arr[k] = R[j]
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j += 1
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k += 1
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# Copy the remaining elements of L[], if there
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# are any
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while i < n1:
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arr[k] = L[i]
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i += 1
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k += 1
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# Copy the remaining elements of R[], if there
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# are any
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while j < n2:
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arr[k] = R[j]
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j += 1
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k += 1
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# l is for left index and r is right index of the
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# sub-array of arr to be sorted
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def mergeSort(arr, l, r):
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if l < r:
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# Same as (l+r)//2, but avoids overflow for
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# large l and h
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m = l+(r-l)//2
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# Sort first and second halves
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mergeSort(arr, l, m)
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mergeSort(arr, m+1, r)
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merge(arr, l, m, r)
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# Driver code to test above
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arr = [12, 11, 13, 5, 6, 7]
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n = len(arr)
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print("Given array is")
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for i in range(n):
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print("%d" % arr[i],end=" ")
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mergeSort(arr, 0, n-1)
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print("\n\nSorted array is")
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for i in range(n):
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print("%d" % arr[i],end=" ")
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