feat: implement while-loop solution

Author: JCPedroza

src/interview-classics/is-palindrome/is-palindrome-method.js

@@ -2,7 +2,7 @@
 const charsToRemove = /[.,:;?!\s]/g
 
 /**
- * Checks if a string is a palindrome.
+ * Checks if a string is a palindrome. Uses srtring and array methods.
  *
  * Time complexity: O(n)
  * Space complexity: O(n)

src/interview-classics/is-palindrome/is-palindrome-while.js

@@ -0,0 +1,44 @@
+// Characters to remove from string in order to normalize it
+const charsToIgnore = /[.,:;?!\s]/
+
+/**
+ * Checks if a string is a palindrome. Uses a while loop.
+ *
+ * Time complexity: O(n)
+ * Space complexity: O(1)
+ *
+ * @param {string} str String to be checked.
+ * @returns {boolean} Whether the string is a palindrome.
+ */
+const isPalindrome = (str) => {
+  let leftIdx = 0
+  let rightIdx = str.length - 1
+
+  while (leftIdx < rightIdx) {
+    // Skip left characters that are in the ignore regex
+    while (charsToIgnore.test(str[leftIdx])) {
+      leftIdx++
+    }
+
+    // Skip right characters that are in the ignore regex
+    while (charsToIgnore.test(str[rightIdx])) {
+      rightIdx--
+    }
+
+    // Different characters, not a palindrome
+    if (str[leftIdx].toLowerCase() !== str[rightIdx].toLowerCase()) {
+      return false
+    }
+
+    // Equal characters, continue to next characters
+    leftIdx++
+    rightIdx--
+  }
+
+  return true
+}
+
+module.exports = {
+  fun: isPalindrome,
+  id: 'while-loop'
+}

src/interview-classics/is-palindrome/is-palindrome.repo.js

@@ -1,5 +1,6 @@
 const algorithms = [
-  require('./is-palindrome-method')
+  require('./is-palindrome-method'),
+  require('./is-palindrome-while')
 ]
 
 module.exports = algorithms

src/interview-classics/is-palindrome/is-palindrome.test.js

@@ -8,33 +8,60 @@ const palindrome = `Anita! LAva :
 
 algorithms.forEach(({ fun, id }) => {
   describe(`Palindrome test algorithm "${id}"`, () => {
-    it('identifies strings that are palindromes', () => {
+    it('identifies palinfromes of length 0', () => {
       assert.equal(
-        fun(palindrome),
+        fun(''),
         true
       )
+    })
 
+    it('identifies palindromes of length 1', () => {
       assert.equal(
-        fun(''),
+        fun('x'),
         true
       )
+    })
 
+    it('identifies small palindromes of even length', () => {
       assert.equal(
         fun('123321'),
         true
       )
     })
 
-    it('identifies strings that are not palindromes', () => {
+    it('identifies small palindromes of odd length', () => {
+      assert.equal(
+        fun('1230321'),
+        true
+      )
+    })
+
+    it('identifies palindromes with multiple whitespace', () => {
+      assert.equal(
+        fun(palindrome),
+        true
+      )
+    })
+
+    it('identifies sentence-like non-palindromes', () => {
       assert.equal(
         fun('This is not a palindrome'),
         false
       )
+    })
 
+    it('identifies one-word non-palindromes of even length', () => {
       assert.equal(
         fun('123123'),
         false
       )
     })
+
+    it('identifies one-word non-palindromes of odd length', () => {
+      assert.equal(
+        fun('1230123'),
+        false
+      )
+    })
   })
 })