added palindromeCheck (trekhleb#806)

* added readme

* added readme

* adding palindromeCheck

* adjusted README

Co-authored-by: Oleksii Trekhleb <trehleb@gmail.com>

README.md

@@ -102,6 +102,7 @@ a set of rules that precisely define a sequence of operations.
   * `A` [Combination Sum](src/algorithms/sets/combination-sum) - find all combinations that form specific sum
 * **Strings**
   * `B` [Hamming Distance](src/algorithms/string/hamming-distance) - number of positions at which the symbols are different
+  * `B` [Palindrome Check](src/algorithms/string/palindrome-check) - is the string the same in reverse
   * `A` [Levenshtein Distance](src/algorithms/string/levenshtein-distance) - minimum edit distance between two sequences
   * `A` [Knuth–Morris–Pratt Algorithm](src/algorithms/string/knuth-morris-pratt) (KMP Algorithm) - substring search (pattern matching)
   * `A` [Z Algorithm](src/algorithms/string/z-algorithm) - substring search (pattern matching)

src/algorithms/string/palindrome-check/README.md

@@ -0,0 +1,25 @@
+# Palindrome Check
+
+A Palindrome is a string that reads the same forwards and backwards. 
+This means that the second half of the string is the reverse of the 
+first half.
+
+## Examples
+
+The following are palindromes (thus would return TRUE):
+
+- "a"
+- "pop"     ->  p + o + p
+- "deed"    ->  de + ed
+- "kayak"   ->  ka + y + ak
+- "racecar" ->  rac + e + car
+
+The following are NOT palindromes (thus would return FALSE):
+
+- "rad"
+- "dodo"
+- "polo"
+
+## References
+
+[GeeksforGeeks - Check if a number is Palindrome](https://www.geeksforgeeks.org/check-if-a-number-is-palindrome/)

src/algorithms/string/palindrome-check/__test__/palindromeCheck.test.js

@@ -0,0 +1,14 @@
+import palindromeCheck from '../palindromeCheck';
+
+describe('palindromeCheck', () => {
+  it('should return whether or not the string is a palindrome', () => {
+    expect(palindromeCheck('a')).toBe(true);
+    expect(palindromeCheck('pop')).toBe(true);
+    expect(palindromeCheck('deed')).toBe(true);
+    expect(palindromeCheck('kayak')).toBe(true);
+    expect(palindromeCheck('racecar')).toBe(true);
+    expect(palindromeCheck('rad')).toBe(false);
+    expect(palindromeCheck('dodo')).toBe(false);
+    expect(palindromeCheck('polo')).toBe(false);
+  });
+});

src/algorithms/string/palindrome-check/palindromeCheck.js

@@ -0,0 +1,17 @@
+/**
+ * @param {string} string
+ * @return {boolean}
+ */
+
+export default function palindromeCheck(string) {
+  let left = 0;
+  let right = string.length - 1;
+  while (left < right) {
+    if (string[left] !== string[right]) {
+      return false;
+    }
+    left += 1;
+    right -= 1;
+  }
+  return true;
+}