2023-02-05 update: added "20. Valid Parentheses"

Author: fartem

README.md

@@ -18,3 +18,4 @@ Profile on LeetCode: [fartem](https://leetcode.com/fartem/).
 | 9. Palindrome Number      | [Link](https://leetcode.com/problems/palindrome-number/)     | [Link](./lib/easy/palindrome_number.dart)     |
 | 13. Roman to Integer      | [Link](https://leetcode.com/problems/roman-to-integer/)      | [Link](./lib/easy/roman_to_integer.dart)      |
 | 14. Longest Common Prefix | [Link](https://leetcode.com/problems/longest-common-prefix/) | [Link](./lib/easy/longest_common_prefix.dart) |
+| 20. Valid Parentheses     | [Link](https://leetcode.com/problems/valid-parentheses/)     | [Link](./lib/easy/valid_parentheses.dart)     |

lib/easy/valid_parentheses.dart

@@ -0,0 +1,32 @@
+// https://leetcode.com/problems/valid-parentheses/
+class Solution {
+  bool isValid(String s) {
+    var stack = [];
+    for (int i = 0; i < s.length; i++) {
+      var c = s[i];
+      switch (c) {
+        case '(':
+        case '{':
+        case '[':
+          stack.insert(0, c);
+          break;
+        case ')':
+          if (stack.isEmpty || stack.removeAt(0) != '(') {
+            return false;
+          }
+          break;
+        case '}':
+          if (stack.isEmpty || stack.removeAt(0) != '{') {
+            return false;
+          }
+          break;
+        case ']':
+          if (stack.isEmpty || stack.removeAt(0) != '[') {
+            return false;
+          }
+          break;
+      }
+    }
+    return stack.isEmpty;
+  }
+}

test/easy/valid_parentheses_test.dart

@@ -0,0 +1,14 @@
+import 'package:leetcode_dart/easy/valid_parentheses.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group(
+    'Example tests',
+    () {
+      final vp = Solution();
+      test('true', () => expect(true, vp.isValid('()')));
+      test('true', () => expect(true, vp.isValid('()[]{}')));
+      test('false', () => expect(false, vp.isValid('(]')));
+    },
+  );
+}