How do I maintain unique items in a list thereby solving this problem?

Question

I require to create a program that provides the solution:

1
3 2
6 5 4
10 9 8 7

using python.

I've been trying out different ideas for over three weeks, and I can't find a solution. All of the code functions/commands that I am permitted to use have been used in the following attempts.

Various attempts include:

The first piece of code shows some promise, but it keeps getting duplicate items in the x list.

    #Attempt 1
    n=4
    l = [0, 1, 2, 3, 4]
    x = [0]
    for i in range (0, n+1):
        k = 0
        j = i
        while k <= i and j != x[j-1]:
            j += l[k]
            print (j, end = " ")
            x.append(j)
            while j != i and j != x[j-1]:
                j -= 1
                if j > i:
                    print (j, end = " ")
                    x.append(j)
            print (x)
            k+=1

    #Attempt 2
    n = 4 
    print (1)
    for a in range (2, n):
        for i in range (2, n*2, a):
            j = i 
            j+=i-1
            print (j, end =" ")
            while j>i:
                j-=1
                print (j, end= " ")
            print ()

    #Attempt 3
    n = 4
    l = [1, 2, 3, 4]
    for i in range (0, n):
        for j in range (0, n*3, l[i]):
            while j >= i:
                print (j, end = " ")
                j-=1
            print ()

The output ought to be

1
3 2
6 5 4
10 9 8 7

in some form or the other, but I never get it.

Some ideas you can consider: the nth line contains n values, and the last of these values is 1+2+...n, which is equal to n*(n+1)/2 — Thierry Lathuille, Jul 19 '19 at 05:38

cdlane · Answer 1 · 2019-07-19T05:48:02.540

3

If you're just looking to get that particular output, knowing only the value of n, then you can do:

n = 8

numbers = range(1, n * (n + 1) // 2 + 1)

for i in range(1, n + 1):
    head, numbers = numbers[:i], numbers[i:]
    print(*reversed(head))

OUTPUT

> python3 test.py
1
3 2
6 5 4
10 9 8 7
15 14 13 12 11
21 20 19 18 17 16
28 27 26 25 24 23 22
36 35 34 33 32 31 30 29
>

Or is there more to this problem that I'm not getting?

edited Jul 19 '19 at 05:48

answered Jul 19 '19 at 05:42

cdlane

40,441
5
32
81

That seems to solve it, BUT I haven't learned that yet, so I can't use that code. Thanks though! – Scaly V Jul 19 '19 at 05:46
1

@ScalyV: 1) I simplifed the answer a bit; 2) how are we supposed to know what you have or have not learned yet? – cdlane Jul 19 '19 at 05:48
I'm sorry, I should have included that. I'll make the edit, but just for you to know, I've used all the commands that I've been taught. But thanks for your code as well! – Scaly V Jul 19 '19 at 07:42

Arvind · Accepted Answer · 2019-07-19T08:46:02.123

1

Answer given by cdlane is more pythonic. This is simplified (school project) version.

n = 4

for i in range(1, n+1):
  max_num_in_line = i * (i+1)// 2  # this gives max number to be printed in line i
  for j in range(i): # here i is the total numbers to be printed in a line.
    print(max_num_in_line, end=' ')
    max_num_in_line -= 1
  print()

edited Jul 19 '19 at 08:46

answered Jul 19 '19 at 05:59

Arvind

1,006
10
16

Helped IMMENSELY. – Scaly V Jul 19 '19 at 07:51

score 0 · Answer 3 · answered Jul 19 '19 at 05:33

0

If you don't want duplicated values you should use set() instead of list() on the x variable.

answered Jul 19 '19 at 05:33

Mahund

21
3

Hey Mahund! I've considered using sets in the past, but since they haven't been covered by our course, I can't use them. – Scaly V Jul 19 '19 at 07:45

How do I maintain unique items in a list thereby solving this problem?

3 Answers3