快速排序算法——两种写法

写法一 伪代码：

快速排序算法：Quicksoft(A, p, r)

p,r分别为数组A的首元素和尾元素的下标
主程序直接调用Quicksort(A, 1, n)即可

输入：数组A[p..r],1≤p≤r≤n
输出：从A[p]到A[r]按照递增顺序排好序的数组A

if p<rthen q←Partition(A, p, q-1) //划分数组，找到首元素A[p]在排好序后的位置q    A[p]←→A[q]    Quicksort(A, p, q-1)    Quicksort(A,q+1,r)

Partition(A, p, r)
输入：数组A[p,r]
数组：j, A的首元素在排好序的数组中的位置

x←A[p]i←pj←r+1while true do    repeat j←j-1    util A[j]≤x    repeat i←i+1    until A[i]>x    if i < j     then A[i]←→A[j]     else return j

Python实现代码：

def quicksort(ar, p, r):    if p < r:        q = partition(ar, p, r)        arr[p], arr[q] = ar[q], arr[p]        quicksort(ar, p, q - 1)        quicksort(ar, q + 1, r)    else:        returndef partition(ar, p, r):    x = ar[p]    i = p    j = r    while 1:        while ar[j] > x:            j = j - 1        while ar[i] <= x:            i = i + 1        if i < j:            ar[i], ar[j] = ar[j], ar[i]        else:            return jarr = [1, 4, 7, 1, 5, 5, 3, 85, 34, 75, 23, 75, 2, 0]print "initial array:\n", arrquicksort(arr, 0, len(arr) - 1)print "result array:\n", arr

写法二 伪代码：

QUICKSORT(A, p, r)

if p<r    q = PARTITION(A,p,r)    QUCIKSORT(A,p,q-1)    QUICKSORT(A,q+1,r)

PARTITION(A, p, r)

x = A[r]i = p-1for j=p to r-1    if A[j]≤x        i = i + 1        exchange A[i] with A[j]exchange A[i+1] with A[r]return i+1

Python实现代码

def quicksort(ar, p, r):    if p < r:        q = partition(ar, p, r)        quicksort(ar, p, q - 1)        quicksort(ar, q + 1, r)    else:        returndef partition(ar, p, r):    x = ar[r]    i = p-1    for j in range(p, r):        if ar[j] <= x:            i = i + 1            ar[i], ar[j] = ar[j], ar[i]    ar[i+1], ar[r] = ar[r], ar[i+1]    print ar    return i+1arr = [2, 8, 7, 1, 3, 5, 6, 4]print "initial array:\n", arrprint "***************************"quicksort(arr, 0, len(arr) - 1)print "***************************"print "result array:\n", arr