Overview

Referencing Algorithm Encyclopedia, we learn about algorithms and data structures.

The implementation is also available on github - bmf-san/road-to-algorithm-master.

Quick Sort

Select an appropriate data (pivot) from the data sequence, and move data smaller than the pivot to the front and data larger than the pivot to the back.
Sort each divided data
A type of divide and conquer method

Computational Time

Worst-case time complexity
- O(n²)
Best-case and average-case time complexity
- O(n log n)

Implementation

package main

import (
	"fmt"
	"math/rand"
)

func quickSort(n []int) []int {
	if len(n) <= 1 {
		return n
	}

	pivot := n[rand.Intn(len(n))]

	low := make([]int, 0, len(n))
	high := make([]int, 0, len(n))
	middle := make([]int, 0, len(n))

	for _, i := range n {
		switch {
		case i < pivot:
			low = append(low, i)
		case i == pivot:
			middle = append(middle, i)
		case i > pivot:
			high = append(high, i)
		}
	}

	low = quickSort(low)
	high = quickSort(high)

	low = append(low, middle...)
	low = append(low, high...)

	return low
}

func main() {
	n := []int{2, 5, 7, 1, 3, 9}
	fmt.Println(quickSort(n))
}