20. https://leetcode.com/problems/valid-parentheses/description/
32. https://leetcode.com/problems/longest-valid-parentheses/description/
22. https://leetcode.com/problems/generate-parentheses/description/
856. https://leetcode.com/problems/score-of-parentheses/description/
301. https://leetcode.com/problems/remove-invalid-parentheses/description/
921. https://leetcode.com/problems/minimum-add-to-make-parentheses-valid/description/
20/32/22/856/301/921 Parentheses 括号匹配或者生成题
原文：https://www.cnblogs.com/keepAC/p/9902856.html