735_asteroid_collision.rb

#Leetcode Problem: https://leetcode.com/problems/asteroid-collision/
# We are given an array asteroids of integers representing asteroids in a row.
#
# For each asteroid, the absolute value represents its size, and the sign represents its direction (positive meaning right, negative meaning left). Each asteroid moves at the same speed.
#
# Find out the state of the asteroids after all collisions. If two asteroids meet, the smaller one will explode. If both are the same size, both will explode. Two asteroids moving in the same direction will never meet.
#
# Example 1:
#
# Input:
# asteroids = [5, 10, -5]
# Output: [5, 10]
# Explanation:
# The 10 and -5 collide resulting in 10.  The 5 and 10 never collide.
#
# Example 2:
#
# Input:
# asteroids = [8, -8]
# Output: []
# Explanation:
# The 8 and -8 collide exploding each other.
#
# Example 3:
#
# Input:
# asteroids = [10, 2, -5]
# Output: [10]
# Explanation:
# The 2 and -5 collide resulting in -5.  The 10 and -5 collide resulting in 10.
#
# Example 4:
#
# Input:
# asteroids = [-2, -1, 1, 2]
# Output: [-2, -1, 1, 2]
# Explanation:
# The -2 and -1 are moving left, while the 1 and 2 are moving right.
# Asteroids moving the same direction never meet, so no asteroids will meet each other.
#
# Note:
# The length of asteroids will be at most 10000.
# Each asteroid will be a non-zero integer in the range [-1000, 1000]..
# ----------------------------------------------------------------------------------------------------------------------
# @param {Integer[]} asteroids
# @return {Integer[]}
require_relative 'core/stack'
def asteroid_collision(asteroids)
  stack = Stack.new

  asteroids.each do |asteroid|
    destroy = false
    if asteroid.positive?
      stack.push asteroid
      next
    else
      while !stack.empty? && stack.top.positive?
        top_element = stack.top
        if top_element < asteroid.abs
          stack.pop
        elsif top_element == asteroid.abs
          destroy = true
          stack.pop
          break
        elsif top_element > asteroid.abs
          break
        end
      end

      if (stack.empty? || stack.top.negative?) && !destroy
        stack.push asteroid
      end
    end
  end
  stack.to_array
end

p asteroid_collision [5, 10, -5]
p asteroid_collision [8, -8]
p asteroid_collision [10, 2, -5]
p asteroid_collision [-2,-1, 1, 2]