def mergeSort(array, start, end): if end - start > 1: middle = (start + end) / 2 mergeSort(array, start, middle) mergeSort(array, middle, end) merge(array, start, middle, middle, end)

The merging of the two halves is done by inserting elements of the second half into the first half. The second half keeps shrinking in size until we are done:

def merge(array, left, leftEnd, right, rightEnd): while left<leftEnd and right<rightEnd: if array[left] > array[right]: array.insert(left, array.pop(right)) right += 1 leftEnd += 1 else: left += 1

Executing the above implementation on 40 random numbers produces the following result:

This implementation is a stable sort. Elements of equal value remain in their original sort order.

Check out more algorithm visualizations at PyAlgoViz.

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