Given a string s containing just the characters ‘(‘, ‘)‘, ‘{‘, ‘}‘, ‘[‘ and ‘]‘, determine if the input string is valid.
An input string is valid if:
Example 1:
Input: s = "()"
Output: true
Example 2:
Input: s = "()[]{}"
Output: true
Example 3:
Input: s = "(]"
Output: false
Example 4:
Input: s = "([)]"
Output: false
Example 5:
Input: s = "{[]}"
Output: true
这种带技巧的题，真的忘了
思路是：先全部push进去，再pop
stack.pop() == null会出异常，所以应该是stack.isEmpty()
最后检查一下stack是否为空
class Solution { public boolean isValid(String s) { //cc if (s == null || s == "") return true; //新建一个stack，遍历s中的每一个元素 Stack<Character> stack = new Stack<Character>(); //返回 for (char c : s.toCharArray()) { if (c == ‘(‘) { stack.push(‘)‘); } else if (c == ‘{‘) { stack.push(‘}‘); } else if (c == ‘[‘) { stack.push(‘]‘); } else { if (stack.pop() == null || stack.pop() != c) return false; } } return stack.isEmpty(); } }
20. Valid Parentheses检验括号字符串的有效性
原文：https://www.cnblogs.com/immiao0319/p/13871778.html