列举至少2种排序算法(如快排),写出实现代码。
def insert_sort(alist): """插入排序""" n = len(alist) # 从第二个位置,即下标为1的元素开始向前插入 for i in range(1, n): # 从第i个元素开始向前比较 for j in range(i, 0, -1): if alist[j-1] > alist[j]: alist[j-1], alist[j] = alist[j], alist[j-1] else: break快速排序
def quick_sort(alist, first, last): """快速排序""" if first >= last: # 递归头 return mid_value = alist[first] low = first high = last while low < high: while low < high and alist[high] >= mid_value: high -= 1 alist[low] = alist[high] while low < high and alist[low] < mid_value: low += 1 alist[high] = alist[low] # 从循环退出时,low == high alist[low] = mid_value # 递归体 # 对low左边的列表执行快速排序 quick_sort(alist, first, low-1) # 对low右边的列表执行快速排序 quick_sort(alist, low+1, last)归并排序
def merge_sort(alist): """归并排序""" n = len(alist) if n <= 1: return alist mid = n//2 left_li = merge_sort(alist[:mid]) right_li = merge_sort(alist[mid:]) # 将两个有序的子序列合并成一个新的整体 return merge(left_li, right_li) def merge(left_li, right_li): """归并排序合并过程""" left_pointer, right_pointer = 0, 0 result = [] while left_pointer < len(left_li) and right_pointer < len(right_li): if left_li[left_pointer] <= right_li[right_pointer]: result.append(left_li[left_pointer]) left_pointer += 1 else: result.append(right_li[right_pointer]) right_pointer += 1 # 退出循环后,两个列表有一个元素已取完(切片操作允许越界,返回空列表) result += left_li[left_pointer:] result += right_li[right_pointer:] return result堆排序
def sift(data, low, high): """堆排序调整过程""" i = low # 根节点 j = 2 * i + 1 # 左子节点 tmp = data[i] # 缓存根节点数据 while j <= high: # 还未到达最后一个叶子结点 if j < high and data[j] < data[j + 1]: # 如果存在右子节点,且右子节点更大 j += 1 # 则此时目标转移到右子节点,接下来根节点与右子节点比较 if data[j] > tmp: # 如果大的子节点数据大于根节点数据,则子节点上位 data[i] = data[j] i = j j = 2 * i + 1 else: # 否则不做调整 break data[i] = tmp # 根节点放置应该放置的数据 def heap_sort(data): """堆排序""" n = len(data) # 建堆 for i in range(n // 2 - 1, -1, -1): # 注:最后一个有子节点的根节点索引为n//2-1 sift(data, i, n - 1) # 挨个出数 for i in range(n - 1, -1, -1): # 堆的规模不断减小 data[0], data[i] = data[i], data[0] # 将堆顶(此时堆中最大的数)的数用堆末的位置存储 sift(data, 0, i - 1) # 调整缩小的堆
def Bubbble_sort(inputSet) if len(inputSet) == 0: return [] sortList = inputSet for i in range(len(sortList) - 1): change_flag = False for i in range(len(sortList) - 1); if sortList[i] > sortList[i+1]: sortList[i], sortList[i+1] = sortList[i+1], sortList[i] change_flag = True if not change_flag: break return sortList
def QuickSort(arr,firstIndex,lastIndex): if firstIndex<lastIndex: divIndex=Partition(arr,firstIndex,lastIndex) QuickSort(arr,firstIndex,divIndex) QuickSort(arr,divIndex+1,lastIndex) else: return def Partition(arr,firstIndex,lastIndex): i=firstIndex-1 for j in range(firstIndex,lastIndex): if arr[j]<=arr[lastIndex]: i=i+1 arr[i],arr[j]=arr[j],arr[i] arr[i+1],arr[lastIndex]=arr[lastIndex],arr[i+1] return i