LeetCode-in-All

238. Product of Array Except Self

Medium

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:

Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)

Solution

# @param {Integer[]} nums
# @return {Integer[]}
def product_except_self(nums)
  product = 1
  ans = Array.new(nums.length, 1)

  nums.each {|num| product *= num}

  nums.each_with_index do |num, i|
    if num != 0
      ans[i] = product / num
    else
      p = 1
      nums.each_with_index {|n, j| p *= n unless j == i}
      ans[i] = p
    end
  end

  ans
end