0238-product-of-array-except-self.rb

# frozen_string_literal: true

# 238. Product of Array Except Self
# https://leetcode.com/problems/product-of-array-except-self
# Medium

=begin
Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i].
The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.
You must write an algorithm that runs in O(n) time and without using the division operation.

Example 1:
Input: nums = [1,2,3,4]
Output: [24,12,8,6]

Example 2:
Input: nums = [-1,1,0,-3,3]
Output: [0,0,9,0,0]

Constraints:
* 2 <= nums.length <= 105
* -30 <= nums[i] <= 30
* The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.
=end

# @param {Integer[]} nums
# @return {Integer[]}
defproduct_except_self(nums)
n=nums.size
out=[1] * n
left=right=1
1.upto(n - 1){ |i|
out[i] *= left *= nums[i - 1]
out[~i] *= right *= nums[-i]
}
out
end

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

require"test/unit"
classTest_length_of_longest_substring < Test::Unit::TestCase
deftest_
assert_equal[24,12,8,6],product_except_self([1,2,3,4])
assert_equal[0,0,9,0,0],product_except_self([-1,1,0, -3,3])
end
end