Generator

Comparisons and swaps at n = 512

Rendered here at the parameters it defaults to, with every essay that calls it — which is the same list as the blast radius of changing it.
Comparisons and swaps at n = 512Selection sort performs the most comparisons of any algorithm here and among the fewest swaps — it never moves an element it does not have to. Ordering these algorithms by comparisons and ordering them by swaps gives two different orders, which is why the question "how many operations" needs the operation named before it has an answer.comparisonsswapsInsertion sort63,071 / 0Selection sort130,816 / 504Bubble sort129,688 / 62,563Merge sort3,964 / 0Heapsort7,653 / 4,170Quicksort5,049 / 2,380n = 512, random inputcounted in the same run

Comparisons and swaps at n = 512

Selection sort performs the most comparisons of any algorithm here and among the fewest swaps — it never moves an element it does not have to. Ordering these algorithms by comparisons and ordering them by swaps gives two different orders, which is why the question "how many operations" needs the operation named before it has an answer.

Drawn at 680 × 380, wide on the page. Everything above is what two-counts returns with no arguments; the caption is the generator's own, computed from the numbers in the drawing rather than written beside it.

36 essays call two-counts. The drawing above is what it returns with no arguments at all; every call below passes it something, because a placement that passes nothing draws whichever member of the family the generator happens to default to rather than the one its essay argues about — which is what optcheck and figfill exist to catch.

Where it is called

Changing this generator changes every one of these figures.

048162432characters every key sharesoperations072,581145,162Character comparisonsRadix sort, characters readElement comparisonsone unit = one character comparisonelement comparisons constant at 3,955 The data that is not a number

The comparison that is not one comparison

every algorithm that makes at most 4 comparisonsthe 24 orderings of 4 elementsroot16 leaves16 seated · 8 with no leafone comparison per level, two outcomes per comparison⌈log₂(4!)⌉ = 5 comparisons The floors

The floor under every comparison sort

comparisons ÷ n log nMerge sort0.855Merge sort with a cutoff0.992Quicksort, random pivot1.018Quicksort, first-element1.082Quicksort, median of three1.117Shellsort1.246Heapsort1.649all of these fit n log n1.9× between best and worst What a bound is

The constant the notation drops

comparisonsswapsInsertion sort63,071 / 0Selection sort130,816 / 504Bubble sort129,688 / 62,563Merge sort3,964 / 0Heapsort7,653 / 4,170Quicksort5,049 / 2,380n = 512, random inputcounted in the same run Counting

One run, four counts, four answers

10³10⁴10³10⁴10⁵ncomparisonsbottom-up (Floyd)repeated insertionn from 128 to 65,536, random input, seeded1.21× between the two at the right-hand edge Structures

Building a heap from the bottom

comparisonsswapsInsertion sort63,071 / 0Selection sort130,816 / 504Bubble sort129,688 / 62,563Merge sort3,964 / 0Heapsort7,653 / 4,170Quicksort5,049 / 2,380n = 512, random inputcounted in the same run Counting

The count somebody chose

481632641281010010³10⁴noperations (mean of 60 runs)Insertion trafficMerge trafficInsertion cmpMerge cmptraffic crossessolid: reads + writes · dashed: comparisonstraffic crosses between n = 12 and 16; comparisons never do What the machine does

Where insertion sort actually wins

4 bytes32 bytes128 bytes512 bytesrecord:QuicksortMerge sortShellsortHeapsortInsertion sortSelection sortBubble sortQuicksortShellsortMerge sortHeapsortSelection sortInsertion sortBubble sortQuicksortShellsortMerge sortSelection sortHeapsortInsertion sortBubble sortSelection sortQuicksortShellsortMerge sortHeapsortInsertion sortBubble sort1234567n = 512, random input, key 8 bytesa read or a write moves the record; a comparison touches the key Counting

The exchange rate nobody wrote down

the language's sortMerge sortlog₂(n!)random43,810 / 43,976nearly sorted10,806 / 24,845already sorted4,095 / 24,576reversed4,095 / 24,576few distinct values27,561 / 42,338n = 4,096, counted through the comparatorthe first column is a fact about the engine, not about sorting Counting

The count that came from somewhere else

0.0000.0100.0200.030150200comparisonsprobability per comparison countmean 139.86exact400 runsn = 32, pivot chosen uniformlysampled mean 140.19 Counting

A distribution computed rather than sampled

every orderthe named inputsmean0102030comparisonsInsertion sort7 to 28 · named inputs reach 28Merge sort12 to 17 · named inputs reach 16Heapsort21 to 29 · named inputs reach 27Quicksort, first-element pivot13 to 28 · named inputs reach 28Quicksort, median of three25 to 29 · named inputs reach 2540,320 orders of 8 distinct elements3 worst cases unnamed Counting

A count over every input

40%60%80%100%8121624324864elements sortedshare of the known worst case the climbs reach, on averageInsertion sort · 20 of 24Merge sort · 24 of 24First-element quicksort · 0 of 24hollow: none reached it24 climbs a size · 100 swaps per elementworst cases known exactly Counting

The worst case found by climbing

0.0010.010.11125102050fraction of positions reshuffled, pmean comparisons, in multiples of the mean on random inputFirst-element quicksort, 81.9×Median-of-three quicksort, 41.4×Insertion sort, 2.0×Merge sort, 1.0××: unshuffled2,048 elements · 12 shuffles a point1 = the mean on random input Counting

A worst case ten positions wide

0102030comparisons on one orderingfloor 16Insertion sort7 to 28 · mean 19.28Merge sort12 to 17 · mean 15.73Heapsort21 to 29 · mean 25.81First-element quicksort13 to 28 · mean 16.92Median-of-three quicksort25 to 29 · mean 26.30Batcher's network19 on all 40,32040,320 orders of 8, enumeratedfloor ⌈log₂ 8!⌉ = 16 Counting

The sort whose count has no distribution

1101001,00010,00010⁵10⁶k, the elements the caller readscomparisonssort all, read kbuild a heap, pop kselect k, sort thoseincremental quicksortkeep the best k while scanningknockout tournamentdashed: the floorlabels at k = 1,00065,536 random distinct keysevery answer checked Counting

The count of the part that was read

Merge sortnone · 55% tiesMerge sort with an insertion cutoffnone · 47% tiesInsertion sortnone · 0% tiesBubble sortnone · 55% tiesShellsort2,014 · 71% tiesHeapsort2,403 · 32% tiesSelection sort1,209 · 24% tiesQuicksort, median-of-three pivot1,428 · 99% tiesequal pairs left out of the order they arrived in4,096 records, 8 distinct keysdark: the sorts that move them Counting

The order equal keys keep

reads and writescache missesRadix sort, 8-bit digitsno comparisonsMerge sort965,752 comparisonsHeapsort1,895,405 comparisonsQuicksort, median-of-three1,187,435 comparisons65,536 keys of 32 bitsdark: the sort that compares nothing Counting

The sort that makes none of them

1416642561k2k4k8k16k33k66k11010010³10⁴10⁵10⁶keys handed backcomparisons no method can go underthe losers, and the outputs' ownorderevery element not handed back losesthe answer is one of n!/(n−k)!sequences65,536 keyseach is a claim about every possible method Counting

Two floors that can be added

0%25%50%75%Merge sort0.0% · 1.03× the floorQuicksort, random pivot0.0% · 1.16× the floorQuicksort, first-element pivot0.0% · 1.18× the floorMerge sort with an insertion cutoff0.0% · 1.31× the floorInsertion sort0.0% · 9.83× the floorShellsort9.8% · 1.31× the floorQuicksort, median-of-three15.4% · 1.18× the floorHeapsort26.2% · 1.45× the floorBubble sort49.2% · 9.83× the floorSelection sort59.9% · 7.77× the floorshare of comparisons whose answer was already implied256 elements, random orderlight: repeats nothing Counting

The questions a sort asks twice

32641282565121010010³10⁴elements sortedword operations a comparison must cost to break evenSelection sort, pairsSelection sort, closureBubble sort, pairsBubble sort, closureHeapsort, pairsHeapsort, closureQuicksort, median-of-three, pairsQuicksort, median-of-three, closuresolid: pairs asked · dashed: everything impliedrandom input · counted exactly Counting

The price of remembering an answer

11010010³10⁴10⁵10⁶k, the number handed backcomparisonstournament, measuredfloor that names the outputsbest earlier floorn = 65,536, one shuffled inputthe floors are worst-case, the count is one input Counting

The comparisons that name the answer

1001000entries in the cacheshare of the repeats it catches0%25%50%75%100%256 entries, one a pair asked in a passSelection sortBubble sortdashed: collisions alonerule at 100%: the table ofevery pair256 random elements · direct-mapped, one pair a slotoccupancy, not distance Counting

The record that forgets on purpose

00.0250.0500.0750.100200300400500comparisonsprobability of exactly that manymerge sort's worst case, 321merge sort, sd 4.22quicksort, sd 36.74n = 64, both exactratio of spreads 8.7 Counting

The spread a merge sort does not have

1,00010010³10⁴10⁵10⁶keys sortedcache missesno recorda cache of 1,024 pairsthe table, written twicethe table, by ordered pairselection sort, 512 lines of 64 bytesexact LRU Counting

The record measured where it would run

4-bit2.97× · mean 2.426-bit2.23× · mean 1.828-bit1.50× · mean 1.2211-bit3.61× · mean 1.5916-bit7.73× · mean 3.23from the counts1.23× · mean 1.06the best for each caseworst over 4 inputs × 2 cachesmisses ÷ the best fixed width's Counting

The digit a pass chooses for itself

1248163264rows in the ringshare of the table's skipped comparisons0%25%50%75%100%256 keys1,024 keys2,048 keysselection sort, random keysticks: expected minima a pass Counting

A record the size of a pass's minima

1282565121,0242,0484,096keys sorted, ntable's skips caught94%96%98%100%the chain of the last passa ring of twelve rowsrandom keys, every answer checkedring: the earlier record, LRU Counting

A record of stretches, not pairs

1282565121,0242,0484,096keys sorted, nrepeats answered94%96%98%100%minimum chain, its own repeatsmaximum chain, its own repeatsone-sided sort's chainrandom keys, every answer checkedeach share of its own side's repeats Counting

Two swaps a pass, and the stretches hold

1282565121,0242,0484,09610³10⁴10⁵10⁶keys sorted, ncomparisons madethe two chainschains and runssorted keys, every answer checkedruns: adjacent positions of known order Counting

A run answers what nobody asked

chains and runsthe same, after a pass over neighboursrandom261,452261,688reversed1,0231,023organ-pipe256,924213,148sorted2,0451,0231,024 keys, the pass's comparisons includedevery answer checked against the keys Counting

A pass repaid by the scans after it

00.500123458shortest run the record keeps, in keyscomparisons a key the pass addsthe pass's own cost, one comparison a key1,024 keys4,096 keys256 keysrandom keys, chains and runs, every answer checkedpass included Counting

The runs too short to drop

keys in each sorted run of the inputreads spent per comparison saved (log scale)1101001,00010,000416642561,024256 keys1,024 keys4,096 keyssolid: two bits a pair · faint: run listreads per comparison saved Counting

What it costs to consult two bits a pair

0124816keys in each sorted run of the inputreads a question: words, or probes of the list48163264128256512sortedone word: the word that holds the first pairrun list, probestwo bits a pair, wordsbehind the filter, words1,024 keys, a pass firstsorted array cut at 24 Counting

A filter that reads the word it saves

keys sortedword reads for each comparison saved (log scale)141664256break-even of a pair table2561,0244,096runs of 4runs of 16runs of 64dashed: without registersa pass firstlogarithmic scale Counting

A run end kept in a register

keys in each sorted run of the inputwords read a question (log scale)0.111048163264128256512sortedregisterskept past a breakanswering from insidetwo bits a pair, plain1,024 keys, a pass firstlogarithmic scale Counting

A register dropped by what it already knew

keys in each sorted run of the inputreads a question (log scale)0.111048163264128256512sortedregisterstwo bits a pair, plainrun list's searchkept through a relearning1,024 keys, a pass firstlogarithmic scale Counting

A register kept through a confirmation

The library, page 5 of 5 — where two-counts sits