how to sort descending order in specific index of list without built-in in python

Question

My problem is this.
1. Input N
2. Input N numbers are entered in the list. For example, N is 5 means 3,2,1,2,4 or 1,2,9,7,5 or 4,2,1,3,8 whatever, N is 3 means 1,2,3 or 7,4,8 or 2,13,26 whatever.

3. Input A and B

4. Sort descending order list only in index A to B. For example, N = 7 , input numbers are 3 2 0 6 7 9 1, A=2, B=5, the output is [3, 2, 9, 7, 6, 0, 1]

my output is like this
[3, 2, 6, 0, 7, 9, 1]
[3, 2, 7, 0, 6, 9, 1]
[3, 2, 9, 0, 6, 7, 1]
[3, 2, 9, 6, 0, 7, 1]
[3, 2, 9, 7, 0, 6, 1]
[3, 2, 9, 0, 7, 6, 1]
[3, 2, 9, 0, 6, 7, 1]

The problem is last 2 output is so weird, I don't know what am i doing wrong.

n = int(input())
list = []
for i in range(n):
    list.append(int(input()))

a = int(input())
b = int(input())
b+=1
tmp=0

for i in range(a,b):
    for j in range(a+1,b):
        if list[i]<list[j]:
            tmp=list[i]
            list[i]=list[j]
            list[j]=tmp
            print(list)

It seems like you're trying to use a selection sort. maybe this can help geeksforgeeks.org/python-program-for-selection-sort — Vishal Singh
– Vishal Singh, Commented Apr 30, 2021 at 7:47

avasuilia · Accepted Answer · 2021-04-30 07:55:04Z

1

You can try the following:

n = int(input())
list = []
for i in range(n):
    list.append(int(input()))

a = int(input())
b = int(input())
b+=1
tmp=0

for i in range(a,b):
    for j in range(i+1,b):
        if list[i]<list[j]:
            tmp=list[i]
            list[i]=list[j]
            list[j]=tmp
            print(list)

answered Apr 30, 2021 at 7:55

avasuilia

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1 Comment

Hongwon Lim Over a year ago

Thanks. a+1 was wrong. really appreciate it

nobleknight · Accepted Answer · 2021-04-30 07:43:41Z

1

You can swap two values in a list like this:

list_[i], list_[j] = list_[j], list_[i]

One suggestion to you: Don't use built-in data-type names as variable names.

answered Apr 30, 2021 at 7:43

nobleknight

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Comments

Carl F. Corneil · Accepted Answer · 2021-04-30 08:07:21Z

0

I would try to simplify this for yourself, and maybe try without loops.

Your list generation, only with added input-directions and changing the list-name to "main":

n = int(input("n:"))
main = []
for i in range(n):
    main.append(int(input(f'{i+1} of {n}:')))
a = int(input("a:"))
b = int(input("b:"))

Now split your list into the respective parts, and use the built in .sort() function.

# Slice into three parts
start = main[:a]
mid = main[a:b+1]
end = main[b+1:]
# Sort the middle, descending
mid.sort(reverse = True)
# Re-combine the lists
main = start + mid + end
print(main)

answered Apr 30, 2021 at 8:07

Carl F. Corneil

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