python選擇排序簡單實現

#!/usr/bin/env python3
# -*- coding: UTF-8 -*-
# Date:2018-5-27
# Author:AreLIN
#選擇排序:每次只取一個最大或最小值的索引

import random

a = []
count_swap = 0
count_iter = 0
#隨機數列表
for _ in range(20):
    a.append(random.randrange(1,101))
print("my first list:\n{}".format(a))

for i in range(len(a)):
    maxindex = i
    for j in range(i+1,len(a)):
        count_iter += 1
        if a[maxindex] < a[j]:
            maxindex = j
    if i != maxindex:
        a[maxindex],a[i] = a[i],a[maxindex]
        count_swap += 1
print("My end list:\n{}  {}  {}".format(a,count_iter,count_swap))

#二元選擇排序：一次取兩個值（最大最小）的索引

a = []
count_swap = 0
count_iter = 0
#隨機數列表
for _ in range(20):
    a.append(random.randrange(1,101))
print("my first list:\n{}".format(a))
for i in range(len(a)//2):
    maxindex = i
    minindex = -i - 1
    minorign = minindex
    for j in range(i+1,len(a)-i):
        count_iter += 1
        if a[maxindex] < a[j]:
            maxindex = j
        if a[minindex] > a[-j-1]:
            minindex = -j - 1
    print("{} {} ".format(maxindex,minindex),end='|')
    if i != maxindex:
        a[maxindex],a[i] = a[i],a[maxindex]
        count_swap += 1
        if (i == minindex) or (i == (len(a) + minindex)):
            minindex = maxindex
    if minorign != minindex:
        a[minindex],a[minorign] = a[minorign],a[minindex]
        count_swap += 1
print("The end list is:\n{},count_swap:{},count_iter:{}".format(a,count_swap,count_iter))

二元選擇排序循環的次數更低，效率更高