用Python写的几个排序算法

用Python练习写一些常用的排序算法

# -*- coding:utf-8 -*-"""选择排序"""def selectSort(arr):    print('this is select sort')    for i in range(0, len(arr)):        min = arr[i]        index = i        for j in range(i + 1, len(arr)):            if(arr[j] < min):                min = arr[j]                index = j        arr[index] = arr[i]        arr[i] = min"""冒泡排序"""def insertSort(arr):    print('this is insert sort')    for i in range(0, len(arr)):        for j in range(i + 1, len(arr)):            if arr[j] < arr[i]:                t = arr[i]                arr[i] = arr[j]                arr[j] = t"""快速排序"""def quickSort(arr, left, right):    if left >= right:        return     i = left    j = right    key = arr[left]    while i < j:        # j向左走，直到找到一个小于key的元素        while i < j and arr[j] >= key:            j -= 1        if i < j:            arr[i] = arr[j]            i += 1        # i向右走，直到找到一个大于key的元素        while i < j and arr[i] <= key:            i += 1        if i < j:            arr[j] = arr[i]            j -= 1    arr[i] = key    quickSort(arr, left, i - 1)    quickSort(arr, i + 1, right)"""归并排序"""def mergeSort(arr, start, end):    if start < end:        mid = (int)((start + end) / 2)        mergeSort(arr, start, mid)        mergeSort(arr, mid + 1, end)        merge(arr, start, mid, mid + 1, end)def merge(arr, s1, e1, s2, e2):    i = s1    j = s2    list = []    while i <= e1 and j <= e2:        if arr[i] <= arr[j]:            list.append(arr[i])            i += 1        else:            list.append(arr[j])            j += 1    while i <= e1:        list.append(arr[i])        i += 1    while j <= e2:        list.append(arr[j])        j += 1     for i in range(s1, max(e1, e2)+1):        arr[i] = list[i-s1]"""堆排序构建一个小顶堆，父节点的值小于孩子节点假设我们需要从海量的数据中找到前k大的数，最好的方法是构建小顶堆首先用前k个数构建一个小顶堆，然后遍历剩余的数如果此数 < 堆顶元素，说明比k个数中的最小值还小，则直接跳过此数，遍历下一个如果此数 > 堆顶元素，则将此数和堆顶交换，然后从堆顶向下调整"""class MinHeap(object):    __max_size = 0; #堆的大小    heap_list = []    # 创建堆    def create_heap(self, arr):        self.heap_list = arr        n = len(self.heap_list)        for i in range(int(n / 2) - 1, -1, -1):            self.fix_down(i, n-1)    # 取出堆顶元素    def get_top(self):        if len(self.heap_list) > 0:            return self.heap_list[0]        return None       # 向下调整堆    def fix_down(self, a, end):        last = end        child = a * 2 + 1 #当前节点的左孩子        temp = self.heap_list[a]        while child <= last:            # 选出两个孩子中较小的那个            if child < last and self.heap_list[child+1] < self.heap_list[child]:                child += 1            if temp < self.heap_list[child]:                break            else:                # 孩子节点覆盖当前节点                self.heap_list[a] = self.heap_list[child]                    a = child                child = child * 2 + 1        self.heap_list[a] = temp        print(self.heap_list)    # 堆排序，取出堆顶元素，与最后一个元素交换，调整堆    def heap_sort(self):        n = len(self.heap_list) - 1        for i in range(n, -1, -1):            temp = self.heap_list[i]            self.heap_list[i] = self.heap_list[0]            self.heap_list[0] = temp            self.fix_down(0, i-1)        return self.heap_listdef heapSort(arr):    m = MinHeap()    m.create_heap(arr)    print('开始排序')    return m.heap_sort() arr = [19, 17, 20, 18, 16, 21]# selectSort(arr)# insertSort(arr)# quickSort(arr, 0, len(arr) - 1)# mergeSort(arr, 0, len(arr) - 1)heapSort(arr)# print(arr)# print(arr)