Add #0020 Valid Parentheses

Author: o-p

difficulty/easy/0020 Valid Parentheses

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+../../problems/0020-valid-parentheses

list/Blind Curated 75/07. Valid Parentheses

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+../../problems/0020-valid-parentheses

problems/0020-valid-parentheses/valid-parentheses.test.ts

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+import isValid from './valid-parentheses';
+
+describe('20. Valid Parentheses', (): void => {
+  test.each`
+       s        | expected
+    ${'()'}     | ${true} }
+    ${'()[]{}'} | ${true}
+    ${'(]'}     | ${false}
+    ${'([)]'}   | ${false}
+    ${'{[]}'}   | ${true}
+  `('Expect $s to be $expected', ({ s, expected }): void =>
+    expect(isValid(s)).toBe(expected)
+  );
+});

problems/0020-valid-parentheses/valid-parentheses.ts

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+interface Match {
+  [left: string]: string;
+}
+
+const DEFAULT_MATCHES: Match = {
+  '(': ')',
+  '[': ']',
+  '{': '}',
+};
+
+/**
+ * 每個字符進入時，可能情況有：
+ *   1. 左括號：在待比對清單中加入對應的右括號
+ *   2. 右括號：如果待比對清單第一個字元跟這個右括號不相同，則錯誤；如果相同，則消去
+ *   3. 其他字：錯誤
+ *
+ * 執行到最後，如果待比對清單已清空，則為正確
+ *
+ * 圖解 isValid('(){[]}')
+ *
+ * 步驟 | 當前字元 | 當前待比對清單 | 比對完之後的待比對清單
+ *   1      (          ''              ')'
+ *   2      )          ')'             ''
+ *   3      {          ''              '}'
+ *   4      [          '}'             ']}'
+ *   5      ]          ']}'            '}'
+ *   6      }          '}'             ''
+ *
+ * 最終待比對清單為空，所以為正確
+ */
+function isValid(s: string, matches: Match = DEFAULT_MATCHES): boolean {
+  let pendings = '';
+  for (const char of s) {
+    if (pendings[0] === char) {
+      pendings = pendings.slice(1);
+      continue;
+    }
+
+    const match = matches[char] ?? null;
+    if (match === null) {
+      return false;
+    }
+
+    pendings = match + pendings;
+  }
+  return pendings.length === 0;
+}
+
+export default isValid;