小魚要學數據結構與算法（基於python)—Day12冒泡排序與選擇排序

排序和查找

一、知識概覽

本章主要講解六種排序算法，知識概覽如下：

1.1 冒泡排序算法

1.2 選擇排序算法

二、代碼實現

2.1冒泡排序

# 冒泡排序代碼
def bubbleSort(alist):
    # 趟數從n-1開始一直到1
    for passnum in range(len(alist) - 1, 0, -1):
        # 每一趟中，比對和交換的範圍
        for i in range(passnum):
            if alist[i] > alist[i + 1]:
                temp = alist[i]
                alist[i] = alist[i + 1]
                alist[i + 1] = temp
                # 也可以寫成alist[i]，alist[i+1]=alist[i+1]，alist[i]


alist = [54, 26, 93, 17, 77, 31]
bubbleSort(alist)
print(alist)

2.2 冒泡排序改進算法

# BS改進，提前退出
def bubbleSort2(alist):
    exchange = True
    passnum = len(alist) - 1
    while passnum > 0 and exchange:
        exchange = False
        for i in range(passnum):
            if alist[i] > alist[i + 1]:
                exchange = True
                temp = alist[i]
                alist[i] = alist[i + 1]
                alist[i + 1] = temp
        passnum = passnum - 1


alist = [54, 26, 93, 17, 77, 31]
bubbleSort2(alist)
print(alist)

2.3 選擇排序算法

#選擇排序
def selectionSort(alist):
    for fillslot in range(len(alist) - 1, 0, -1):
        positionOfMax=0
        for location in range(1,fillslot+1):
            if alist[location]>alist[positionOfMax]:
                positionOfMax=location
        temp=alist[fillslot]
        alist[fillslot]=alist[positionOfMax]
        alist[positionOfMax]=temp
alist = [54, 26, 93, 17, 77, 31]
selectionSort(alist)
print(alist)

2.4 輸出結果

[17, 26, 31, 54, 77, 93]
[17, 26, 31, 54, 77, 93]
[17, 26, 31, 54, 77, 93]