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| − | <pre>
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| − | from random import choices
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| − | def group_by_color(data, start, stop, color):
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| − | operations_counter = 0
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| − | while start < stop and start < len(data) and stop >= 0:
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| − | # data[start] is equal to examine(data[start]) except swap function call
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| − | while start < len(data) and data[start] == color: # Finding first element with incorrect color from start
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| − | start += 1 # Element with correct color already on right position, moving forward
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| − | operations_counter += 1
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| − | while start < stop and stop >= 0 and data[stop] != color: # Finding first element with correct color from end
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| − | stop -= 1 # Element with incorrect color will be swapped later or keep on that position, moving backward
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| − | operations_counter += 1
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| − | if start < stop:
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| − | data[start], data[stop] = data[stop], data[start] # Equal to swap(start, stop)
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| − | operations_counter += 1
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| − | assert operations_counter <= len(data) * 2 # Check O(2*n) restriction
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| − | return start # Return last element with specified color
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| − | colors_list = choices(['red', 'white', 'blue'], k=100)
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| − | red_ending = group_by_color(colors_list, 0, len(colors_list) - 1, 'red') # Sort red O(n)
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| − | group_by_color(colors_list, red_ending + 1, len(colors_list) - 1, 'white') # Sort white O(n)
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| − | # Blue already sorted
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| − | </pre>
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| − | First pass: group red elements from 0 to k. Swapping not red elements found from begin and red elements found from end.
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| − | Second pass: group white elements from k to j. Swapping not white elements from k and white elements from end.
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| − | Blue elements already grouped from j to n.
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| − | --[[User:Bkarpov96|Bkarpov96]] ([[User talk:Bkarpov96|talk]]) 17:36, 19 June 2020 (UTC)
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