The Selection Sort

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−1 passes to sort n items, since the final item must be in place after the (n−1) st pass.

def selectionSort(alist):
for fillslot in range (len(alist)-1,0,-1):
#从后往前循环
#[8,7,6,5,4,3,2,1]#列
positionOfMax=0#最大值的位置为0

for location in range(1,fillslot+1):#行，内部查找
if alist[location]>alist[positionOfMax]:
#找到最大值，然后最大值的位置为找到数字的位置
positionOfMax=location
#对调
temp = alist[fillslot]
alist[fillslot] = alist[positionOfMax]
alist[positionOfMax] = temp

alist = [54,26,93,17,77,31,44,55,20]
selectionSort(alist)
print(alist)

1）循环第一次，先找到最大/最小值，把最小值放在第一位，或者最大的放最后。

2）循环第二次，找到第二小的数字，放在最小值的后面的数字对调

3）以此类推

def select_sort(ary):
n = len(ary)
for i in range(0,n):
min = i                             #最小元素下标标记
for j in range(i+1,n):
if ary[j] < ary[min] :
min = j                     #找到最小值的下标
ary[min],ary[i] = ary[i],ary[min]   #交换两者
return ary

Q-49: Suppose you have the following list of numbers to sort: [11, 7, 12, 14, 19, 1, 6, 18, 8, 20] which list represents the partially sorted list after three complete passes of selection sort?

[11, 7, 12, 14, 8, 1, 6, 18, 19, 20]