From ecde337d9bab5665169c161f88345e0230a25226 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Sat, 19 Dec 2020 20:18:22 -0800
Subject: [PATCH] Add better solution - O(n) time and space

---
 .../get_products_of_all_other_elements.rb     | 62 +++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/data_structures/arrays/get_products_of_all_other_elements.rb b/data_structures/arrays/get_products_of_all_other_elements.rb
index 8bfe4a6..b4a8a2f 100644
--- a/data_structures/arrays/get_products_of_all_other_elements.rb
+++ b/data_structures/arrays/get_products_of_all_other_elements.rb
@@ -21,3 +21,65 @@ def calculate_products_of_all_other_elements(nums)
 end
 
 puts(calculate_products_of_all_other_elements([1, 2, 3]))
+
+# 2. O(n) time and space
+# Arrays - Get Products of all other elements in Ruby
+
+# Generates prefix products
+def build_prefix_products(nums)
+  prefix_products = []
+
+  nums.each do |num|
+    if prefix_products.count > 0
+      prefix_products << (prefix_products.last * num)
+    else
+      prefix_products << num
+    end
+  end
+
+  return prefix_products
+end
+
+# Generates suffix products
+def build_suffix_products(nums)
+  suffix_products = []
+
+  nums.reverse.each do |num|
+    if suffix_products.count > 0
+      suffix_products << (suffix_products.last * num)
+    else
+      suffix_products << num
+    end
+  end
+
+  return suffix_products
+end
+
+# Builds output
+def output(prefix_products, suffix_products, nums)
+  result = []
+
+  nums.reverse.each_with_index do |num, index|
+    if index == 0
+      result << suffix_products[index + 1]
+    elsif index == nums.length - 1
+      result << prefix_products[index - 1]
+    else
+      result << (prefix_products[index - 1] * suffix_products[index + 1])
+    end
+  end
+
+  return result
+end
+
+# Generate result from the product of prefixes and suffixes
+def products(nums)
+  prefix_products = build_prefix_products(nums)
+  suffix_products = build_suffix_products(nums)
+  suffix_products = suffix_products.reverse
+
+  return output(prefix_products, suffix_products, nums)
+end
+
+puts(products([1, 2, 3]))
+# => [6, 3, 2]