ConstructShell.md

Construct Shell

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A 2D list lst of size 2 * n - 1 is called a shell if it is filled with zeros and has the following configuration:

• lst[0] contains one element;
• lst[1] contains two elements;
• ...
• lst[n - 2] contains n - 1 elements;
• lst[n - 1] contains n elements;
• lst[n] contains n - 1 elements;
• ...
• lst[2 * n - 3] contains two elements;
• lst[2 * n - 2] contains one element.

Given an integer n, return a shell list.

Example

For n = 3, the output should be

solution(n) = [[0],
                     [0, 0],
                     [0, 0, 0],
                     [0, 0],
                     [0]]

Input/Output

• [execution time limit] 4 seconds (py3)

• [input] integer n

  An integer defining the size of the shell.

  Guaranteed constraints:
  1 ≤ n ≤ 30.

• [output] array.array.integer

  A shell.

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Solution

def solution(n):
    return [[0 for x in range(y+1)] for y in range (n-1)] + [[0 for x in range(y+1)] for y in range (n)][::-1]

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