# Polyphase merge sort

Additionally, once a comparison function is written, any sort can be used without modification, non-comparison sorts typically require specialized versions for each datatype. Stepping back to the previous iteration, we were reading from 1 and 2. Most implementations produce a sort, which means that the implementation preserves the input order of equal elements in the sorted output. Otherwise, in the more common case where the number of runs is not known in advance, "near optimal" distribution algorithms are used.

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Although the judges only had 2, words on their list, Donald found 4, words, as prizes, the school received a new television and enough candy bars for all of his schoolmates to eat. The current output file will become an input file for the next iteration. The algorithm can also be implemented in a recursive way, the idea is that to sort an array of n elements, A, one first orders the subarray A and then inserts the last element.

Seward, in many large applications needing speed, polyohase computer radix sort is an improvement on comparison sorts. Both algorithms were invented in the late s by Prof. We start with polphase runs, then we copy those runs to 2 input tapes on the left on the pic beloweach iteration we take two different runs from the input tapes, merge and sort them, and in one iteration save them to the first output tape, and in next iteration - to the second one, as shown below.

At this point, Knuth received support from Richard S. A sequence of numbers and the Cartesian tree derived from them.

In this sense, mergesort, heapsort, and introsort are asymptotically optimal in terms of the number of comparisons they must perform, non-comparison sorts can achieve O performance by using operations other than comparisons, allowing them to sidestep this lower bound. Elements pointed to by blue arrow are compared and the smaller element is moved to its final position pointed to by red arrow.

The Art of Computer Programming — The Art of Computer Programming is a comprehensive monograph written by Donald Knuth that covers many kinds of programming algorithms and their analysis. The closed form follows from the master theorem, in the worst case, the number of comparisons merge sort polyphsae is equal to or slightly smaller than, which is between and.

## Polyphase merge sort

File 1 just emptied and became the new output file. Mfrge a ProxmapSort is complete, ProxmapSearch can be used to find keys in the array in O time if the keys were well distributed during the sort.

Shellsort, also known as Shell sort or Shell's method, is an in-place comparison sort. This algorithm works for all arrays, including those smaller than 64, concurrently with the search for runs, the runs are merged with merge sort.

### algorithm - Polyphase merge sort - what is the number of phases - Stack Overflow

All red elements are smaller than blue here, Pairs of consecutive sequence values shown as the thick red edges that bracket a sequence value x the darker blue point. Looking at the perfect 3 file case, the number of runs for merged working backwards: Displacement cycle for list "bdeac", when shifting the first letter b to its correct position:.

When they are sorted with a non-stable sort, the 5s may end up in the opposite order in the sorted output. The sort algorithm must gain enough information from the comparisons to identify the correct permutation, if the algorithm always completes after at most f steps, it cannot distinguish more than 2f cases because the keys are distinct and each comparison has only two possible outcomes.

In many practical cases, long runs are present. Megge, Using a carefully chosen mapKey function, divide the A2 into subarrays using the keys in A Disperse, Read over A, dropping each key into its bucket in A2, insertion sorting as needed. When the end of one of the N-1 working files is reached, then it becomes the new output file and what was the output file becomes one of the N-1 working input files, starting a new iteration of polyphase merge sort.

So one of my motivations was to put straight a story that had been very badly told, bythe first three volumes and part one of volume four of his series had polyphwse published 2. Merge sort Cascade merge sort Oscillating merge sort Polyphase merge sort. Records were stored on magnetic tape and processed on banks of magnetic tape drives, such as these IBM s.

A polyphase merge sort is a variation of bottom up Merge sort that sorts a list using an initial uneven distribution of sub-lists runsprimarily used for external sortingand is more efficient than an ordinary merge sort when there are less than 8 external working files such as a tape drive or a file on a hard drive.

Otherwise, in the more common case where the number of runs is not known in advance, "near optimal" distribution algorithms are used. A polyphase merge sort is not a stable sort. With 4 files, the first iteration creates runs of size 3 original runs, the second iteration 5 original runs, the third iteration 9 original runs and so on, following the Fibonacci like pattern, 1, 3, 5, 9, 17, 31, 57, Such exploits made Knuth a topic of discussion among the mathematics department, Knuth started to write a book about compiler design inand soon realized that the scope of the book needed to be much larger.

In practice, the input file will not have the exact number of runs needed for a perfect distribution. File 1 just emptied and became the new output file.

## 1 thoughts on “Polyphase merge sort”

1. Mausho

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