From dc533283a2a3c5743fae1548210f8968fb7a8d08 Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Thu, 1 Apr 2021 09:36:46 -0700
Subject: [PATCH 1/3] Add hash table approach

---
 data_structures/hash_table/anagram_checker.rb | 73 ++++++++++++++++++-
 1 file changed, 71 insertions(+), 2 deletions(-)

diff --git a/data_structures/hash_table/anagram_checker.rb b/data_structures/hash_table/anagram_checker.rb
index 1158134..0d0f2f6 100644
--- a/data_structures/hash_table/anagram_checker.rb
+++ b/data_structures/hash_table/anagram_checker.rb
@@ -17,8 +17,6 @@
 #
 # Approach: Hash table
 #
-
-# 
 # Complexity analysis:
 #
 # Time complexity: O(n). Time complexity is O(n) since accessing the counter
@@ -60,3 +58,74 @@ s = 'a'
 t = 'ab'
 puts(is_anagram(s, t))
 # => false
+
+
+def is_anagram(s, t)
+  s_length = s.length
+  t_length = t.length
+  counter = Hash.new(0)
+
+  return false unless s_length == t_length
+
+  (0...s_length).each do |i|
+    counter[s[i]] += 1
+  end
+
+  (0...s_length).each do |i|
+    counter[t[i]] -= 1
+
+    return false if counter[t[i]] < 0
+  end
+
+  true
+end
+
+s = 'anagram'
+t = 'nagaram'
+puts(is_anagram(s, t))
+# => true
+
+s = 'rat'
+t = 'car'
+puts(is_anagram(s, t))
+# => false
+
+s = 'a'
+t = 'ab'
+puts(is_anagram(s, t))
+# => false
+
+#
+# Approach 2: Hash table
+#
+
+# Algorithm: we could also first increment the counter for s,
+# then decrement the counter for t. If at any point the counter
+# drops below zero, we know that t contains an extra letter,
+# not in s, and return false immediately.
+
+# Complexity analysis:
+#
+# Time complexity: O(n).
+# Space complexity: O(1).
+#
+
+def is_anagram(s, t)
+  s_length = s.length
+  t_length = t.length
+  counter = Hash.new(0)
+
+  return false unless s_length == t_length
+
+  (0...s_length).each do |i|
+    counter[s[i]] += 1
+  end
+
+  (0...s_length).each do |i|
+    counter[t[i]] -= 1
+
+    return false if counter[t[i]] < 0
+  end
+
+  true
+end

From 44c32084541b2679161577a1257d1454d4f4752d Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Thu, 1 Apr 2021 09:36:52 -0700
Subject: [PATCH 2/3] Add another hash table approach

---
 data_structures/hash_table/anagram_checker.rb | 35 +++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/data_structures/hash_table/anagram_checker.rb b/data_structures/hash_table/anagram_checker.rb
index 0d0f2f6..16fc429 100644
--- a/data_structures/hash_table/anagram_checker.rb
+++ b/data_structures/hash_table/anagram_checker.rb
@@ -129,3 +129,38 @@ def is_anagram(s, t)
 
   true
 end
+
+#
+# Approach 3: populate 2 hashes and compare them
+#
+
+def is_anagram(s, t)
+  s = s.chars
+  t = t.chars
+
+  return false if s.count != t.count
+
+  hash1 = {}
+  s.chars.each do |value|
+    hash1[value] = if hash1[value]
+                     hash1[value] + 1
+                   else
+                     1
+                   end
+  end
+
+  hash2 = {}
+  t.chars.each do |value|
+    hash2[value] = if hash2[value]
+                     hash2[value] + 1
+                   else
+                     1
+                   end
+  end
+
+  hash1.keys.each do |key|
+    return false if hash2[key] != hash1[key]
+  end
+
+  true
+end

From 434e72a4f7cc0cd977e98c941449e492929e1d2f Mon Sep 17 00:00:00 2001
From: Vitor Oliveira <vbrazo@gmail.com>
Date: Thu, 1 Apr 2021 09:38:27 -0700
Subject: [PATCH 3/3] Add very simple tests

---
 data_structures/hash_table/anagram_checker.rb | 34 +++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/data_structures/hash_table/anagram_checker.rb b/data_structures/hash_table/anagram_checker.rb
index 16fc429..abbb209 100644
--- a/data_structures/hash_table/anagram_checker.rb
+++ b/data_structures/hash_table/anagram_checker.rb
@@ -130,6 +130,21 @@ def is_anagram(s, t)
   true
 end
 
+s = 'anagram'
+t = 'nagaram'
+puts(is_anagram(s, t))
+# => true
+
+s = 'rat'
+t = 'car'
+puts(is_anagram(s, t))
+# => false
+
+s = 'a'
+t = 'ab'
+puts(is_anagram(s, t))
+# => false
+
 #
 # Approach 3: populate 2 hashes and compare them
 #
@@ -141,7 +156,7 @@ def is_anagram(s, t)
   return false if s.count != t.count
 
   hash1 = {}
-  s.chars.each do |value|
+  s.each do |value|
     hash1[value] = if hash1[value]
                      hash1[value] + 1
                    else
@@ -150,7 +165,7 @@ def is_anagram(s, t)
   end
 
   hash2 = {}
-  t.chars.each do |value|
+  t.each do |value|
     hash2[value] = if hash2[value]
                      hash2[value] + 1
                    else
@@ -164,3 +179,18 @@ def is_anagram(s, t)
 
   true
 end
+
+s = 'anagram'
+t = 'nagaram'
+puts(is_anagram(s, t))
+# => true
+
+s = 'rat'
+t = 'car'
+puts(is_anagram(s, t))
+# => false
+
+s = 'a'
+t = 'ab'
+puts(is_anagram(s, t))
+# => false