Valid Palindrome

Author: casentino

valid-palindrome/casentino.ts

@@ -0,0 +1,38 @@
+function isPalindrome(s: string): boolean {
+  let start = 0;
+  let last = s.length - 1;
+  while (start < last) {
+    while (start < last && !isAlphanumeric(s.charAt(start))) {
+      start += 1;
+    }
+    while (start < last && !isAlphanumeric(s.charAt(last))) {
+      last -= 1;
+    }
+    if (s.charAt(start).toLowerCase() !== s.charAt(last).toLowerCase()) {
+      return false;
+    }
+    start += 1;
+    last -= 1;
+  }
+  return true;
+}
+
+function isAlphanumeric(character: string) {
+  const characterCode = character.charCodeAt(0);
+  const lowerStart = "a".charCodeAt(0);
+  const lowerEnd = "z".charCodeAt(0);
+  const upperStart = "A".charCodeAt(0);
+  const upperEnd = "Z".charCodeAt(0);
+  const numericStart = "0".charCodeAt(0);
+  const numericEnd = "9".charCodeAt(0);
+  if (upperStart <= characterCode && upperEnd >= characterCode) {
+    return true;
+  }
+  if (lowerStart <= characterCode && lowerEnd >= characterCode) {
+    return true;
+  }
+  if (numericStart <= characterCode && numericEnd >= characterCode) {
+    return true;
+  }
+  return false;
+}