From e70ba583a280f0dd62f16b16496035a07fcf91a4 Mon Sep 17 00:00:00 2001
From: Jessica Kwok <jessicatckwok@gmail.com>
Date: Mon, 22 Mar 2021 08:07:14 -0700
Subject: [PATCH] Add solution using hash map

---
 data_structures/arrays/single_number.rb | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/data_structures/arrays/single_number.rb b/data_structures/arrays/single_number.rb
index 5c68747..f639857 100644
--- a/data_structures/arrays/single_number.rb
+++ b/data_structures/arrays/single_number.rb
@@ -9,8 +9,26 @@
 # @param {Integer[]} nums
 # @return {Integer}
 
+# 
+# Approach 1: Hash map
+#
+# Time Complexity: O(n)
+#
 def single_number(nums)
+  result_hash = {}
+  nums.each do |num|
+    if result_hash[num]
+      result_hash[num] +=1 
+    else
+      result_hash[num] = 1
+    end
+  end
+  
+  result_hash.each do |k, v|
+    return k if v == 1
+  end
 end
+
 nums = [2, 2, 1]
 puts(single_number(nums))
 # Output: 1