add: validPalindrome solution

Author: Cyjin-jani

valid-palindrome/Cyjin-jani.js

@@ -0,0 +1,41 @@
+// naive한 풀이
+// tc: O(n)
+// sc: O(n)
+const isPalindromeNaive = function (s) {
+  const str = s.toLowerCase().replace(/[^a-z0-9]/g, ''); // 이 부분에서 공간복잡도가 O(n)
+  let leftIdx = 0;
+  let rightIdx = str.length - 1;
+
+  while (leftIdx <= rightIdx) {
+    if (str[leftIdx] !== str[rightIdx]) {
+      return false;
+    } else {
+      leftIdx++;
+      rightIdx--;
+    }
+  }
+  return true;
+};
+
+// 좀 더 최적화 된 풀이
+// tc: O(n)
+// cs: O(1)
+const isPalindrome = function (s) {
+  let leftIdx = 0;
+  let rightIdx = s.length - 1;
+
+  while (leftIdx < rightIdx) {
+    while (leftIdx < rightIdx && !isAlphaNumeric(s[leftIdx])) leftIdx++;
+    while (leftIdx < rightIdx && !isAlphaNumeric(s[rightIdx])) rightIdx--;
+
+    if (s[leftIdx].toLowerCase() !== s[rightIdx].toLowerCase()) return false;
+
+    leftIdx++;
+    rightIdx--;
+  }
+  return true;
+};
+
+function isAlphaNumeric(char) {
+  return /[a-zA-Z0-9]/.test(char);
+}