125. Valid Palindrome

Author: remy727

README.md

@@ -66,6 +66,7 @@
 | 113 | Path Sum II | [Ruby](./algorithms/ruby/0113-path-sum-ii.rb) | Medium |
 | 121 | Best Time to Buy and Sell Stock | [Ruby](./algorithms/ruby/0121-best-time-to-buy-and-sell-stock.rb) | Easy |
 | 122 | Best Time to Buy and Sell Stock II | [Ruby](./algorithms/ruby/0122-best-time-to-buy-and-sell-stock-ii.rb) | Medium |
+| 125 | Valid Palindrome | [Ruby](./algorithms/ruby/0125-valid-palindrome.rb) | Easy |
 | 129 | Sum Root to Leaf Numbers | [Ruby](./algorithms/ruby/0129-sum-root-to-leaf-numbers.rb) | Medium |
 | 133 | Clone Graph | [Ruby](./algorithms/ruby/0133-clone-graph.rb) | Medium |
 | 134 | Gas Station | [Ruby](./algorithms/ruby/0134-gas-station.rb) | Easy |

algorithms/ruby/0125-valid-palindrome.rb

@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+
+# 125. Valid Palindrome
+# https://leetcode.com/problems/valid-palindrome
+# Easy
+
+=begin
+A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.
+
+Given a string s, return true if it is a palindrome, or false otherwise.
+
+Example 1:
+Input: s = "A man, a plan, a canal: Panama"
+Output: true
+Explanation: "amanaplanacanalpanama" is a palindrome.
+
+Example 2:
+Input: s = "race a car"
+Output: false
+Explanation: "raceacar" is not a palindrome.
+
+Example 3:
+Input: s = " "
+Output: true
+Explanation: s is an empty string "" after removing non-alphanumeric characters.
+Since an empty string reads the same forward and backward, it is a palindrome.
+
+Constraints:
+1 <= s.length <= 2 * 105
+s consists only of printable ASCII characters.
+=end
+
+# @param {String} s
+# @return {Boolean}
+def is_palindrome(s)
+  filtered_s = s.gsub(/[^a-bA-Z0-9]/i, "").downcase
+  left, right = 0, filtered_s.size - 1
+
+  while left < right
+    return false if filtered_s[left] != filtered_s[right]
+    left += 1
+    right -= 1
+  end
+
+  true
+end
+
+# **************** #
+#       TEST       #
+# **************** #
+
+require "test/unit"
+class Test_is_palindrome < Test::Unit::TestCase
+  def test_
+    assert_equal true, is_palindrome("A man, a plan, a canal: Panama")
+    assert_equal false, is_palindrome("race a car")
+    assert_equal true, is_palindrome("")
+  end
+end