Selection Sort

最新推荐文章于 2024-12-31 22:29:56 发布

JoeCLWu

最新推荐文章于 2024-12-31 22:29:56 发布

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CC 4.0 BY-SA版权

本文链接：https://blog.youkuaiyun.com/JoeCLWu/article/details/81132537

本文介绍了一种改进版的冒泡排序——选择排序算法，并通过一个示例程序详细展示了其工作原理。选择排序通过每次遍历只进行一次交换来提高效率，每完成一次遍历则将当前未排序部分的最大元素放置到正确的位置。

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def selectionSort(alist):
    a = len(alist)-1
    while a > 0:
        flag = 0
        for i in range(0,a+1):
            if alist[i] > alist[flag]:
                flag = i
        alist[a], alist[flag] = alist[flag], alist[a]
        a -=1

alist = [1,20,17,2,33,11111,454,3244,12222222]
selectionSort(alist)
print(alist)

The selection sort improves on the bubble sort by making only one exchange for every pass through the list. In order to do this, a selection sort looks for the largest value as it makes a pass and, after completing the pass, places it in the proper location. As with a bubble sort, after the first pass, the largest item is in the correct place. After the second pass, the next largest is in place. This process continues and requires n−1n−1passes to sort n items, since the final item must be in place after the (n−1)(n−1) st pass.

Figure 3 shows the entire sorting process. On each pass, the largest remaining item is selected and then placed in its proper location. The first pass places 93, the second pass places 77, the third places 55, and so on.