标签：div 算法 排序 表示 range base 初始 比较 print
核心思想：取一个初始值，将数组中比该值小的放在其左边，比其大的放在右边， 再对左、右子数组进行相同操作，直到数组排好序。
def quicksort(nums): l = 0 r = len(nums) - 1 _quicksort(nums,l,r) def _quicksort(nums,l,r): if l < r: p = partition(nums,l,r) _quicksort(nums,l,p-1) _quicksort(nums,p+1,r) def partition(nums,l,r): base = nums[l] j = l+1 for i in range(l+1,r+1): if nums[i]<base: nums[i],nums[j]=nums[j],nums[i] j+=1 nums[l],nums[j-1]=nums[j-1],nums[l] return j-1 nums = [6,2,5,3,4,8,1,7] quicksort(nums) print(nums)
改进：随机选择初始值，避免数组有序使算法退化。从两边开始遍历，减少遍历时间。
import random def quicksort(nums): l = 0 r = len(nums) - 1 _quicksort(nums,l,r) def _quicksort(nums,l,r): if l < r: p = partition(nums,l,r) _quicksort(nums,l,p-1) _quicksort(nums,p+1,r) def partition(nums, l, r): ind = random.randint(l, r) nums[l], nums[ind] = nums[ind], nums[l] base = nums[l] i, j = l+1, r while True: while i <= r and nums[i] < base: # 不能改为nums[i] <= base i += 1 while j >= l + 1 and nums[j] > base: # 不能改为nums[j] >= base. j -= 1 if i > j: break else: nums[i], nums[j] = nums[j], nums[i] i += 1 j -= 1 nums[j], nums[l] = nums[l], nums[j] return j nums = [6,2,5,3,4,8,1,7] quicksort(nums) print(nums)
改进：三路快排，用于解决数组中有较多重复的值。
import random def quicksort(nums): l = 0 r = len(nums) - 1 _quicksort(nums,l,r) def _quicksort(nums,l,r): if l < r: lt,gt = partition(nums,l,r) _quicksort(nums,l,lt-1) _quicksort(nums,gt,r) def partition(nums, l, r): ind = random.randint(l, r) nums[l], nums[ind] = nums[ind], nums[l] base = nums[l] lt = l # nums[l+1...lt] < base gt = r + 1 # nums[gt...r] > base i = l + 1 # nums[lt+1...i] == base while (i < gt): # i==gt时表示已经比较结束 if (nums[i] < base): nums[i], nums[lt+1] = nums[lt+1], nums[i] lt += 1 i += 1 elif (nums[i] > base): nums[i], nums[gt-1] = nums[gt-1], nums[i] gt -= 1 else: # nums[i] == base i += 1 nums[l], nums[lt] = nums[lt], nums[l] return lt, gt nums = [6,2,5,3,4,8,1,7] quicksort(nums) print(nums)
标签：div 算法 排序 表示 range base 初始 比较 print
原文地址：https://www.cnblogs.com/xiximayou/p/12332816.html
