二元選擇排序

在簡單選擇排序的基礎上，一輪中同時比較出最大值與最小值

lst1 = [
    [1, 8, 9, 5, 6, 7, 4, 3, 2],
    [9, 8, 7, 6, 5, 4, 3, 2, 1],
    [1, 2, 3, 4, 5, 6, 7, 8, 9],
    [1, 1, 1, 1, 3, 1, 1, 1, 2]
]
nums = lst1[0]
length = len(nums)
print(nums)
count_iter = 0  #叠代計數器
count_swap = 0  #發生交換的次數計數器
for i in range(length//2):
    maxindex = i
    minindex = -i -1
    minorigin = minindex
    for j in range(i + 1, length - i): #每次左右都要少比較一個
        count_iter += 1
        if nums[j] > nums[maxindex]:
            maxindex = j
        if nums[-j - 1] < nums[minindex]:
            minindex = -j - 1
    #print(maxindex, minindex)
    if maxindex != i:
        nums[maxindex], nums[i] = nums[i], nums[maxindex]
        count_swap += 1
        if i == minindex or i == length + minindex:
            minindex = maxindex
    if minorigin != minindex:
        nums[minorigin], nums[minindex] = nums[minindex], nums[minorigin]
        count_swap += 1
print(nums, count_iter, count_swap)

輸出結果：

[1, 8, 9, 5, 6, 7, 4, 3, 2]
[9, 8, 7, 6, 5, 4, 3, 2, 1] 20 6

算法（三）二元選擇排序