The shelf that settles

Problem

Nayeli tidies up her stationery shop before closing. On the shelf, each slot either holds a box or is empty, and she wants to see how everything looks once the boxes go all the way down: no box changes column, each one only drops until it hits the bottom of the shelf or another box.

Write a function that takes shelf, a list of strings of the same length: the first string is the top row and the last one the bottom row, # is a box and . an empty slot. The shelf is at most 8 rows by 8 slots, and it may come in empty or with empty rows.

Return a new list of strings, the same size, with the boxes already fallen.

With ["#.#", "..#", ".#."] the first column holds one box and the second another one, and both end up in the bottom row; the third holds two, which end up in the two bottom rows. You return ["...", "..#", "###"].

Examples

• The example

  ["#.#", "..#", ".#."] → ["...", "..#", "###"]

• The shelf with no boxes

  ["...", "...", "..."] → ["...", "...", "..."]

• The full shelf

  ["###", "###", "###"] → ["###", "###", "###"]

• It was already settled

  ["...", "..#", "###"] → ["...", "..#", "###"]

• A single box at the very top

  ["#..", "...", "..."] → ["...", "...", "#.."]

• A shelf of a single row

  ["#.#"] → ["#.#"]

• A shelf of a single column

  ["#", ".", "#", "."] → [".", ".", "#", "#"]

• Two boxes apart in the same column

  ["#..", "...", "#..", ".#."] → ["...", "...", "#..", "##."]

Besides these, the challenge has hidden tests that are revealed when you submit your solution.

You start with this

def settle_shelf(shelf):
    pass

function settleShelf(shelf) {
}