1706-where-will-the-ball-fall.rb

# frozen_string_literal: true

# 1706. Where Will the Ball Fall
# https://leetcode.com/problems/where-will-the-ball-fall

=begin

You have a 2-D grid of size m x n representing a box, and you have n balls. The box is open on the top and bottom sides.

Each cell in the box has a diagonal board spanning two corners of the cell that can redirect a ball to the right or to the left.

A board that redirects the ball to the right spans the top-left corner to the bottom-right corner and is represented in the grid as 1.
A board that redirects the ball to the left spans the top-right corner to the bottom-left corner and is represented in the grid as -1.
We drop one ball at the top of each column of the box. Each ball can get stuck in the box or fall out of the bottom. A ball gets stuck if it hits a "V" shaped pattern between two boards or if a board redirects the ball into either wall of the box.

Return an array answer of size n where answer[i] is the column that the ball falls out of at the bottom after dropping the ball from the ith column at the top, or -1 if the ball gets stuck in the box.

### Example 1:
Input: grid = [[1,1,1,-1,-1],[1,1,1,-1,-1],[-1,-1,-1,1,1],[1,1,1,1,-1],[-1,-1,-1,-1,-1]]
Output: [1,-1,-1,-1,-1]
Explanation: This example is shown in the photo.
Ball b0 is dropped at column 0 and falls out of the box at column 1.
Ball b1 is dropped at column 1 and will get stuck in the box between column 2 and 3 and row 1.
Ball b2 is dropped at column 2 and will get stuck on the box between column 2 and 3 and row 0.
Ball b3 is dropped at column 3 and will get stuck on the box between column 2 and 3 and row 0.
Ball b4 is dropped at column 4 and will get stuck on the box between column 2 and 3 and row 1.

### Example 2:
Input: grid = [[-1]]
Output: [-1]
Explanation: The ball gets stuck against the left wall.

### Example 3:
Input: grid = [[1,1,1,1,1,1],[-1,-1,-1,-1,-1,-1],[1,1,1,1,1,1],[-1,-1,-1,-1,-1,-1]]
Output: [0,1,2,3,4,-1]

### Constraints:
* m == grid.length
* n == grid[i].length
* 1 <= m, n <= 100
* grid[i][j] is 1 or -1.

=end

# @param {Integer[][]} grid
# @return {Integer[]}
def find_ball(grid)
  total_col = grid.first.size

  0.upto(total_col - 1).map do |index_col|
    grid.each do |row|
      if row[index_col] == 1 && row[index_col + 1] == 1
        index_col += 1
      elsif row[index_col] == -1 && row[index_col - 1] == -1 && index_col > 0
        index_col -= 1
      else
        index_col = -1
        break
      end
    end

    index_col
  end
end

# **************** #
#       TEST       #
# **************** #

require "test/unit"
class Test_find_ball < Test::Unit::TestCase
  def test_
    assert_equal [1, -1, -1, -1, -1], find_ball([[1, 1, 1, -1, -1], [1, 1, 1, -1, -1], [-1, -1, -1, 1, 1], [1, 1, 1, 1, -1], [-1, -1, -1, -1, -1]])
    assert_equal [-1], find_ball([[-1]])
    assert_equal [0, 1, 2, 3, 4, -1], find_ball([[1, 1, 1, 1, 1, 1], [-1, -1, -1, -1, -1, -1], [1, 1, 1, 1, 1, 1], [-1, -1, -1, -1, -1, -1]])
  end
end