golang 快速排序

Posted 2021-05-24

func partition(A []int, p, r int) int {
	x, i := A[r-1], p
	for j := p; j < r-1; j++ {
		if A[j] <= x {
			A[i], A[j] = A[j], A[i]
			i++
		}
	}
	A[i], A[r-1] = A[r-1], A[i]
	return i
}

// QuickSort O(nlgn)
func QuickSort(A []int, p, r int) {
	if p+1 < r {
		q := partition(A, p, r)
		QuickSort(A, p, q)
		QuickSort(A, q+1, r)
	}
}

import "math/rand"

func partition(A []int, p, r int) int {
	x, i := A[r-1], p
	for j := p; j < r-1; j++ {
		if A[j] <= x {
			A[i], A[j] = A[j], A[i]
			i++
		}
	}
	A[i], A[r-1] = A[r-1], A[i]
	return i
}

func randPartition(A []int, p, r int) int {
	i := rand.Intn(r-p) + p
	A[i], A[r-1] = A[r-1], A[i]
	return partition(A, p, r)
}

// RandQuickSort O(nlgn)
func RandQuickSort(A []int, p, r int) {
	if p+1 < r {
		q := randPartition(A, p, r)
		RandQuickSort(A, p, q)
		RandQuickSort(A, q+1, r)
	}
}

import "math/rand"

func partition(A []int, p, r int) int {
	x, i := A[r-1], p
	for j := p; j < r-1; j++ {
		if A[j] <= x {
			A[i], A[j] = A[j], A[i]
			i++
		}
	}
	A[i], A[r-1] = A[r-1], A[i]
	return i
}

func randPartition(A []int, p, r int) int {
	i := rand.Intn(r-p) + p
	A[i], A[r-1] = A[r-1], A[i]
	return partition(A, p, r)
}

// RandQuickSortGo O(nlgn)
func RandQuickSortGo(A []int, p, r int, chans chan<- int) {
	if p+1 < r {
		q := randPartition(A, p, r)
		if r-p > 1000 {
			c := make(chan int, 2)
			go RandQuickSortGo(A, p, q, c)
			go RandQuickSortGo(A, q+1, r, c)
			for i := 0; i < 2; i++ {
				<-c
			}
		} else {
			RandQuickSortGo(A, p, q, nil)
			RandQuickSortGo(A, q+1, r, nil)
		}
	}
	if chans != nil {
		chans <- 0
	}
}

import "math/rand"

func partitionSameElement(A []int, p, r int) (int, int) {
	x, i, j := A[r-1], p, r
	for k := p; k < j; k++ {
		if A[k] <= x {
			A[i], A[k] = A[k], A[i]
			if A[i] != x {
				i++
			}
		} else if A[k] > x {
			j--
			A[j], A[k] = A[k], A[j]
		}
	}
	return i, j
}

func randPartitionSameElement(A []int, p, r int) (int, int) {
	i := rand.Intn(r-p) + p
	A[i], A[r-1] = A[r-1], A[i]
	return partitionSameElement(A, p, r)
}

// RandQuickSortSameElement O(nlgn)
func RandQuickSortSameElement(A []int, p, r int) {
	if p+1 < r {
		q, t := randPartitionSameElement(A, p, r)
		RandQuickSortSameElement(A, p, q)
		RandQuickSortSameElement(A, t, r)
	}
}

import "math/rand"

func partitionSameElement(A []int, p, r int) (int, int) {
	x, i, j := A[r-1], p, r
	for k := p; k < j; k++ {
		if A[k] <= x {
			A[i], A[k] = A[k], A[i]
			if A[i] != x {
				i++
			}
		} else if A[k] > x {
			j--
			A[j], A[k] = A[k], A[j]
		}
	}
	return i, j
}

func randPartitionSameElement(A []int, p, r int) (int, int) {
	i := rand.Intn(r-p) + p
	A[i], A[r-1] = A[r-1], A[i]
	return partitionSameElement(A, p, r)
}

// TailRescursiveQuickSort O(nlgn)
func TailRescursiveQuickSort(A []int, p, r int) {
	for p+1 < r {
		q, t := randPartitionSameElement(A, p, r)
		TailRescursiveQuickSort(A, p, q)
		p = t
	}
}

用golang刷算法--快速排序算法

快速排序算法流程

1. 选定一个基准值(任意选,以第一个为例)
2. 定义左右指针指向左右两端
3. 左指针往右移动,如果遇到大于基准值的数就把它和右指针的值调换位置,然后左指针不动,右指针开始向左移动,如果遇到小于基准值的数就把他和左指针的值调换位置,然后开始移动左指针,以此类推,知道左右指针相遇
4. 递归上述过程知道排序结束

用golang实现

func QuickSort(intList []int) {
	// 如果长度小于等于1就直接结束
	if len(intList) <= 1 {
		return
	}
	// 1. 将第一个值选定为基准值
	flag := intList[0]
	// 定义左右指针
	left, right := 0, len(intList)-1

	for i := 1; i <= right; {
		if intList[i] > flag {
			intList[i], intList[right] = intList[right], intList[i]
			right--
		}else{
			intList[i], intList[left] = intList[left], intList[i]
			i++
			left++
		}
	}
	// 递归
	QuickSort(intList[:left])
	QuickSort(intList[left+1:])
}