Learn in the textbookSearch and Sorting Algorithms
DefinitionQuick sort (クイックソート) chooses one pivot value, splits the data into a group smaller than it and a group larger than it, and repeats the same steps on each group.
ExplanationOnce a group has one element or none, there is nothing left to split, and lining up the groups in order sorts the whole set. Applying the same procedure to smaller and smaller parts like this is called recursion. On average it needs fewer comparisons than the square-type methods, but a poor choice of pivot pushes the count toward the square of the number of items.
AnalogyIt is like splitting a pile of papers into those dated before a reference date and those after it, then splitting each pile the same way again.
Memory hookQuick, as the name says: on average it is fast.