python学习之实现5种排序算法

Posted 2021-07-14 今夜月色很美

冒泡排序

from timeit import Timer


# 冒泡排序
# 每轮循环比较交换相邻两个数的值，把最大值放在末尾，就像冒泡
def bubble_sort(arr):
    for i in range(len(arr)):
        for j in range(len(arr) - i - 1):
            if arr[j] > arr[j + 1]:
                # print("i=%s,j=%s,%s" % (i, j, arr))
                arr[j], arr[j + 1] = arr[j + 1], arr[j]
    return arr


print(bubble_sort([986, 980, 125, 605, 787, 211, 849, 21, 643, 97, 88, 433, 705, 392, 954, 264, 499, 0, 838, 745]))
t1 = Timer("bubble_sort([388, 794, 673, 566, 219, 428, 64, 716, 39, 432, 249, 877, 222, 339, 943, 76, 25, 822, 13, "
           "446])", "from __main__ import bubble_sort")

# 20个随机数排列整齐，10000次排序完成需要时间约0.2666784
print(t1.timeit(10000))

选择排序

from timeit import Timer


# 选择排序
# 每轮循环选出最大值放在末尾
def select_sort(arr):
    for i in range(len(arr)):
        max_index = 0
        for j in range(0, len(arr) - i):
            # print("i=%s,j=%s,max_index=%s,%s" % (i, j, max_index, arr))
            if arr[j] > arr[max_index]:
                max_index = j
        arr[len(arr) - i - 1], arr[max_index] = arr[max_index], arr[len(arr) - i - 1]
    return arr


print(select_sort([986, 980, 125, 605, 787, 211, 849, 21, 643, 97, 88, 433, 705, 392, 954, 264, 499, 0, 838, 745]))
time = Timer("select_sort([388, 794, 673, 566, 219, 428, 64, 716, 39, 432, 249, 877, 222, 339, 943, 76, 25, 822, 13, "
             "446])", "from __main__ import select_sort")
# 20个随机数排列整齐，10000次排序完成需要时间约0.193074
print(time.timeit(10000))

插入排序

from timeit import Timer


# 插入排序
# 先使前n个数有序，然后逐个加入元素
def insert_sort(arr):
    # order_last有序列表最后一个数的下标
    order_last = 0
    for i in range(1, len(arr)):
        value = arr[i]
        # 从后往前遍历有序列表的每个元素，如果比新加入元素大，则向后移动一位
        for j in range(order_last, -1, -1):
            # print("i=%s,j=%s,%s" % (i, j, arr))
            if arr[j] > value:
                arr[j + 1] = arr[j]
                arr[j] = value
        # 内层循环结束，有序列表多了一个元素，最后一个数的下标往后移
        order_last = order_last + 1
    return arr


print(insert_sort([986, 980, 125, 605, 787, 211, 849, 21, 643, 97, 88, 433, 705, 392, 954, 264, 499, 0, 838, 745]))
time = Timer("insert_sort([388, 794, 673, 566, 219, 428, 64, 716, 39, 432, 249, 877, 222, 339, 943, 76, 25, 822, 13, "
             "446])", "from __main__ import insert_sort")
# 20个随机数排列整齐，10000次排序完成需要时间约0.204921
print(time.timeit(10000))

归并排序

from timeit import Timer


# 归并排序
# 递归分成左右两个子集，直至每个子集元素个数为1，然后将左右子集有序merge
def merge_sort(arr):
    if len(arr) > 1:
        merged = []
        # 第一步，分裂
        mid = len(arr) // 2
        # print("原数组：%s, mid=%s,左子集：%s,右子集：%s" % (arr, mid, arr[:mid], arr[mid:]))
        left_arr = merge_sort(arr[:mid])
        right_arr = merge_sort(arr[mid:])
        # print("排序后：%s, mid=%s,左子集：%s,右子集：%s" % (arr, mid, arr[:mid], arr[mid:]))
        # 第二步，合并
        while left_arr and right_arr:
            if left_arr[0] < right_arr[0]:
                merged.append(left_arr.pop(0))
            else:
                merged.append(right_arr.pop(0))
        merged.extend(left_arr if left_arr else right_arr)
        # print("合并后：%s" % merged)
        return merged
    else:
        return arr


print(merge_sort([986, 980, 125, 605, 787, 211, 849, 21, 643, 97, 88, 433, 705, 392, 954, 264, 499, 0, 838, 745]))
time = Timer("merge_sort([388, 794, 673, 566, 219, 428, 64, 716, 39, 432, 249, 877, 222, 339, 943, 76, 25, 822, 13, "
             "446])", "from __main__ import merge_sort")
# 20个随机数排列整齐，10000次排序完成需要时间0.2543816
print(time.timeit(10000))

快速排序

from timeit import Timer


# 快速排序
# 每轮循环选出最大值放在末尾
def quick_sort(arr, left, right):
    if left >= right:
        return arr
    # 取列表中的第一个数做中值
    mid = arr[left]
    start = left + 1
    end = right
    while start <= end:
        while start <= end and arr[start] <= mid:
            start = start + 1

        while start <= end and arr[end] >= mid:
            end = end - 1

        if start > end:
            break
        else:
            arr[start],arr[end] = arr[end],arr[start]
    # print("before====mid=%s,left=%s,right=%s,%s" % (left, left, right, arr))
    arr[left],arr[end] = arr[end],arr[left]
    # print("after====mid=%s,left=%s,right=%s,%s" % (end, left, right, arr))
    quick_sort(arr, left, end - 1)
    quick_sort(arr, end + 1, right)
    return arr


print(quick_sort([986, 980, 125, 605, 787, 211, 849, 21, 643, 97, 88, 433, 705, 392, 954, 264, 499, 0, 838, 745], 0, 19))
time = Timer("quick_sort([388, 794, 673, 566, 219, 428, 64, 716, 39, 432, 249, 877, 222, 339, 943, 76, 25, 822, 13, "
             "446], 0, 19)", "from __main__ import quick_sort")
# 20个随机数排列整齐，10000次排序完成需要时间0.1195915
print(time.timeit(10000))