Update 125-Valid-Palindrome.js

Author: aakhtar3

javascript/125-Valid-Palindrome.js

@@ -1,54 +1,77 @@
 /**
+ * Array - Filter && Clone && Reverse
+ * Time O(N) | Space O(N)
  * https://leetcode.com/problems/valid-palindrome/
- * Time O(N^2) | Space O(1)
  * @param {string} s
  * @return {boolean}
  */
-var isPalindrome = function (s) {
+var isPalindrome = function(s) {
     if (!s.length) return true;
+    
+    const alphaNumeric = filterAlphaNumeric(s);/* Time O(N) | Space O(N) */
+    const reversed = reverse(alphaNumeric);    /* Time O(N) | Space O(N) */
+    
+    return alphaNumeric === reversed;
+};
+
+const filterAlphaNumeric = (s, nonAlphaNumeric = new RegExp('[^a-z0-9]','gi')) => s
+    .toLowerCase()               /* Time O(N) | Space O(N) */
+    .replace(nonAlphaNumeric, '')/* Time O(N) | Space O(N) */
 
-    s = s.toLowerCase();
+const reverse = (s) => s
+    .split('')/* Time O(N) | Space O(N) */
+    .reverse()/* Time O(N) | Space O(N) */
+    .join('');/* Time O(N) | Space O(N) */
 
-    return isValid(s);
+/**
+ * 2 Pointer | Midde Convergence
+ * Time O(N) | Space O(1)
+ * https://leetcode.com/problems/valid-palindrome/
+ * @param {string} s
+ * @return {boolean}
+ */
+var isPalindrome = function(s) {
+    if (!s.length) return true;
+
+    return isValid(s);/* Time O(N) */
 };
 
 const isValid = (s) => {
-    let [left, right] = [0, s.length - 1];
+    let [ left, right ] =  [ 0, (s.length - 1) ];
 
-    while (left < right) {
-        while (left < right && isNonAlphaNumeric(s[left])) left++;
-        while (left < right && isNonAlphaNumeric(s[right])) right--;
+    while (left < right) {                          /* Time O(N) */
+        [ left, right ] = moveToMid(s, left, right);/* Time O(N) */
 
-        const isSame = s[left] === s[right];
-        if (!isSame) return false;
+        const [ leftCode, rightCode ] = getCodes(s, left, right);
+  
+        const isEqual = leftCode === rightCode;
+        if (!isEqual) return false;
 
-        left++;
-        right--;
+        left++; right--;
     }
 
     return true;
-};
+}
 
-const isNonAlphaNumeric = (char) => {
-    const isNonAlpha = char < 'a' || 'z' < char; // a(97) - z(122)
-    const isNonNumeric = char < '0' || '9' < char; // 0(48) - 9(57)
+const moveToMid = (s, left, right) => {
+    while ((left < right) && !isAlphaNumeric(s[left])) left++;  /* Time O(N) */
+    while ((left < right) && !isAlphaNumeric(s[right])) right--;/* Time O(N) */
+    
+    return [ left, right ];
+}
 
-    return isNonAlpha && isNonNumeric;
-};
+const getCodes = (s, left, right) => [ getCode(s[left]), getCode(s[right]) ];
 
-/**
- * https://leetcode.com/problems/valid-palindrome/
- * Time O(N) | Space O(N)
- * @param {string} s
- * @return {boolean}
- */
-var isPalindrome = function(s) {
-    if (!s.length) return true;
-    
-    s = s.toLowerCase();
-    s = s.replace(/[^a-z0-9]/gi, '');
-    
-    let reversed = s.split('').reverse().join('');
+const getCode = (char) => char.toLowerCase().charCodeAt(0);
+
+const isAlphaNumeric = (char) => {
+    const code = getCode(char);
 
-    return reversed === s;
+    const [ a, z ] = [ 97, 122 ];
+    const isAlpha = (a <= code) && (code <= z);
+
+    const [ zero, nine ] = [ 48, 57 ];
+    const isNumeric = (zero <= code) && (code <= nine);
+
+    return isAlpha || isNumeric;
 };