20. 有效的括号

https://leetcode-cn.com/problems/valid-parentheses/

Java

/*
 * @Author: Goog Tech
 * @Date: 2020-07-16 20:45:04
 * @Description: https://leetcode-cn.com/problems/valid-parentheses/
 * @FilePath: \leetcode-googtech\#20. Valid Parentheses\Solution.java
 */ 
class Solution {
    public boolean isValid(String s) {
        // 初始化栈
        Stack<Character> stack = new Stack<Character>();
        // 遍历字符串,逐个比较字符
        for(char c:s.toCharArray()){
            // 将左括号压入栈中
            if(c=='('){
                stack.push(')');
            }else if(c=='['){
                stack.push(']');
            }else if(c=='{'){
                stack.push('}');
            // 弹出左括号并与右括号相比较
            }else if(stack.isEmpty()||c!=stack.pop()){
                return false;
            }
        }
        // 如果左右括号全部匹配完毕则栈为空
        return stack.isEmpty();
    }
}

Python

'''
@Author: Goog Tech
@Date: 2020-07-16 20:45:17
@Description: https://leetcode-cn.com/problems/valid-parentheses/
@FilePath: \leetcode-googtech\#20. Valid Parentheses\Solution.py
'''
class Solution(object):
    def isValid(self, symbolString):
        """
        :type s: str
        :rtype: bool
        """
        index = 0
        stack = []
        opens = "([{"
        closers = ")]}"
        balanced = True
        # 遍历字符串中的字符(括号)
        while index < len(symbolString) and balanced:
            symbol = symbolString[index]
            # 将左括号压入栈中
            if symbol in opens:
                stack.append(symbol)
            else:
                # 如果栈不为空,弹出左括号并于右括号比较
                if stack:
                    top = stack.pop()
                    if opens.index(top) != closers.index(symbol):
                        balanced = False
                else:
                    balanced = False                 
            index = index + 1
        # 如果栈不为空或balanced为False,则匹配失败
        if stack or not balanced:
            return False
        else:
            return True

print(Solution().isValid("{[()]}")) # Test: True