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Concept
Tri par paquets
Résumé
Bucket sort, or bin sort, is a sorting algorithm that works by distributing the elements of an array into a number of buckets. Each bucket is then sorted individually, either using a different sorting algorithm, or by recursively applying the bucket sorting algorithm. It is a distribution sort, a generalization of pigeonhole sort that allows multiple keys per bucket, and is a cousin of radix sort in the most-to-least significant digit flavor. Bucket sort can be implemented with comparisons and therefore can also be considered a comparison sort algorithm. The computational complexity depends on the algorithm used to sort each bucket, the number of buckets to use, and whether the input is uniformly distributed.
Bucket sort works as follows:
Set up an array of initially empty "buckets".
Scatter: Go over the original array, putting each object in its bucket.
Sort each non-empty bucket.
Gather: Visit the buckets in order and put all elements back into the original array.
function bucketSort(array, k) is
buckets ← new array of k empty lists
M ← 1 + the maximum key value in the array
for i = 0 to length(array) do
insert array[i] into buckets[floor(k × array[i] / M)]
for i = 0 to k do
nextSort(buckets[i])
return the concatenation of buckets[0], ...., buckets[k]
Let array denote the array to be sorted and k denote the number of buckets to use. One can compute the maximum key value in linear time by iterating over all the keys once. The floor function must be used to convert a floating number to an integer ( and possibly casting of datatypes too ). The function nextSort is a sorting function used to sort each bucket. Conventionally, insertion sort is used, but other algorithms could be used as well, such as selection sort or merge sort. Using bucketSort itself as nextSort produces a relative of radix sort; in particular, the case n = 2 corresponds to quicksort (although potentially with poor pivot choices).
When the input contains several keys that are close to each other (clustering), those elements are likely to be placed in the same bucket, which results in some buckets containing more elements than average.
Source officielle
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