feat: add valid palindrome solution

Author: sandrig

README.md

@@ -15,6 +15,7 @@
 | 9   | [Maximum Product of Three Numbers](https://leetcode.com/problems/maximum-product-of-three-numbers/) | [TypeScript](https://github.com/sandrig/leetcode/blob/master/typescript/src/maximumProductofThreeNumbers/README.md) | _O(nlogn)_ | _O(1)_         | Array, Math, Sorting                                    |
 | 10  | [Maximum Average Subarray I](https://leetcode.com/problems/maximum-average-subarray-i/)             | [TypeScript](https://github.com/sandrig/leetcode/blob/master/typescript/src/maximumAverageSubarrayI/README.md)      | _O(n)_     | _O(1)_         | Array, Sliding Window                                   |
 | 11  | [Intersection of Two Arrays II](https://leetcode.com/problems/intersection-of-two-arrays-ii/)       | [TypeScript](https://github.com/sandrig/leetcode/blob/master/typescript/src/intersectionOfTwoArraysII/README.md)    | _O(n + m)_ | _O(min(n, m))_ | Array, Hash Table, Two Pointers, Binary Search, Sorting |
+| 12  | [Valid Palindrome II](https://leetcode.com/problems/valid-palindrome-ii/)                           | [TypeScript](https://github.com/sandrig/leetcode/blob/master/typescript/src/validPalindromeII/README.md)            | _O(n)_     | _O(1)_         | Two Pointers, String Greedy                             |
 
 ## Medium
 

typescript/src/validPalindromeII/README.md

@@ -0,0 +1,65 @@
+# [Valid Palindrome II](https://leetcode.com/problems/valid-palindrome-ii/)
+
+## Description
+
+Given a string **s**, return **true** if the **s** can be palindrome after deleting at most one character from it.
+
+**Example 1:**
+
+```
+Input: s = "aba"
+Output: true
+```
+
+**Example 2:**
+
+```
+Input: s = "abca"
+Output: true
+Explanation: You could delete the character 'c'.
+```
+
+**Example 3:**
+
+```
+Input: s = "abc"
+Output: false
+```
+
+## Solution
+
+```typescript
+function validPalindrome(s: string): boolean {
+  function isPalindromeRange(start: number, end: number): boolean {
+    while (start < end) {
+      if (s[start] !== s[end]) {
+        return false;
+      }
+      start++;
+      end--;
+    }
+    return true;
+  }
+
+  let left = 0;
+  let right = s.length - 1;
+
+  while (left < right) {
+    if (s[left] !== s[right]) {
+      // Try skipping the left character or the right character
+      return (
+        isPalindromeRange(left + 1, right) || isPalindromeRange(left, right - 1)
+      );
+    }
+    left++;
+    right--;
+  }
+
+  return true;
+}
+```
+
+## Complexity Analysis
+
+- Time complexity: _O(n)_
+- Space complexity: _O(1)_

typescript/src/validPalindromeII/validPalindrome.test.ts

@@ -0,0 +1,24 @@
+import { validPalindrome } from "./validPalindrome";
+
+describe("Valid Palindrome II", () => {
+  it("should return true for a valid palindrome", () => {
+    expect(validPalindrome("aba")).toBe(true);
+    expect(validPalindrome("abccba")).toBe(true);
+    expect(validPalindrome("racecar")).toBe(true);
+    expect(validPalindrome("deified")).toBe(true);
+  });
+
+  it("should return true for a valid palindrome when one character is removed", () => {
+    expect(validPalindrome("abca")).toBe(true);
+    expect(validPalindrome("abcba")).toBe(true);
+    expect(validPalindrome("abccbad")).toBe(true);
+    expect(validPalindrome("radarz")).toBe(true);
+  });
+
+  it("should return false when more than one character is removed", () => {
+    expect(validPalindrome("abcde")).toBe(false);
+    expect(validPalindrome("levellee")).toBe(false);
+    expect(validPalindrome("radarza")).toBe(false);
+    expect(validPalindrome("racecarara")).toBe(false);
+  });
+});

typescript/src/validPalindromeII/validPalindrome.ts

@@ -0,0 +1,28 @@
+export function validPalindrome(s: string): boolean {
+  function isPalindromeRange(start: number, end: number): boolean {
+    while (start < end) {
+      if (s[start] !== s[end]) {
+        return false;
+      }
+      start++;
+      end--;
+    }
+    return true;
+  }
+
+  let left = 0;
+  let right = s.length - 1;
+
+  while (left < right) {
+    if (s[left] !== s[right]) {
+      // Try skipping the left character or the right character
+      return (
+        isPalindromeRange(left + 1, right) || isPalindromeRange(left, right - 1)
+      );
+    }
+    left++;
+    right--;
+  }
+
+  return true;
+}