Create: 0125-valid-palindrome.dart

Author: NikSWE

Diff for: dart/0125-valid-palindrome.dart

@@ -0,0 +1,32 @@
+// Time Complexity: O(n)
+// Space Complexity: O(1)
+
+class Solution {
+  static bool isAlphaNum(String s) {
+    if ((s.codeUnits[0] >= 'a'.codeUnitAt(0) &&
+            s.codeUnits[0] <= 'z'.codeUnitAt(0)) ||
+        (s.codeUnits[0] >= 'A'.codeUnitAt(0) &&
+            s.codeUnits[0] <= 'Z'.codeUnitAt(0)) ||
+        (s.codeUnits[0] >= '0'.codeUnitAt(0) &&
+            s.codeUnits[0] <= '9'.codeUnitAt(0))) {
+      return true;
+    }
+    return false;
+  }
+
+  bool isPalindrome(String s) {
+    var left = 0, right = s.length - 1;
+
+    while (left < right) {
+      while (!Solution.isAlphaNum(s[left]) && left < right) left++;
+      while (!Solution.isAlphaNum(s[right]) && left < right) right--;
+
+      if (s[left].toLowerCase() != s[right].toLowerCase()) return false;
+
+      left++;
+      right--;
+    }
+
+    return true;
+  }
+}