feat: add a solution for S0125

README.md

@@ -39,6 +39,7 @@ Contributions are welcome! If you have a more efficient solution or want to add
 | 83     | Remove Duplicates from Sorted List                     | 0 ms    | 43.5 MB  | [Problem](src/main/java/com/anthonyschuijlenburg/S0083/Problem.md) |
 | 88     | Merge Sorted Array                                     | 0 ms    | 41.8 MB  | [Problem](src/main/java/com/anthonyschuijlenburg/S0088/Problem.md) |
 | 94     | Binary Tree Inorder Traversal                          | 0 ms    | 41.3 MB  | [Problem](src/main/java/com/anthonyschuijlenburg/S0094/Problem.md) |
+| 125    | Valid Palindrome <- Could improve                      | 15 ms   | 44.8 MB  | [Problem](src/main/java/com/anthonyschuijlenburg/S0125/Problem.md) |
 | 206    | Reverse Linked List                                    | 1 ms    | 42.4 MB  | [Problem](src/main/java/com/anthonyschuijlenburg/S0206/Problem.md) |
 | 506    | Relative Ranks <- Needs work!                          | 27 ms   | 45.4 MB  | [Problem](src/main/java/com/anthonyschuijlenburg/S0506/Problem.md) |
 | 786    | K-th Smallest Prime Fraction <- Needs work!            | 672 ms  | 106.5 MB | [Problem](src/main/java/com/anthonyschuijlenburg/S0786/Problem.md) |

src/main/java/com/anthonyschuijlenburg/S0125/Problem.md

@@ -0,0 +1,32 @@
+# 125. Valid Palindrome
+
+Topics: Two Pointers , String
+
+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.
+

src/main/java/com/anthonyschuijlenburg/S0125/Solution.java

@@ -0,0 +1,9 @@
+package com.anthonyschuijlenburg.S0125;
+
+public class Solution {
+    public boolean isPalindrome(String s) {
+        s = s.replaceAll("[^a-zA-Z0-9]", "").toLowerCase();
+
+        return new StringBuilder(s).reverse().toString().equals(s);
+    }
+}

src/test/java/com/anthonyschuijlenburg/S0125/SolutionTest.java

@@ -0,0 +1,41 @@
+package com.anthonyschuijlenburg.S0125;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class SolutionTest {
+
+    @Test
+    void isPalindrome_testCase0() {
+        Solution solutionGenerator = new Solution();
+
+        boolean result = solutionGenerator.isPalindrome("");
+        assertTrue(result);
+    }
+
+    @Test
+    void isPalindrome_testCase1() {
+        Solution solutionGenerator = new Solution();
+
+        boolean result = solutionGenerator.isPalindrome("A man, a plan, a canal: Panama");
+        assertTrue(result);
+    }
+
+    @Test
+    void isPalindrome_testCase2() {
+        Solution solutionGenerator = new Solution();
+
+        boolean result = solutionGenerator.isPalindrome("racecar");
+        assertTrue(result);
+    }
+
+    @Test
+    void isPalindrome_testCase3() {
+        Solution solutionGenerator = new Solution();
+
+        boolean result = solutionGenerator.isPalindrome("race a car");
+        assertFalse(result);
+    }
+}