Leetcode: 20. Valid Parentheses

Description

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

思路

• 栈
• 左括号都入栈
• 遇到右括号时，判断栈顶和它是否匹配，不匹配，直接返回，匹配，出栈

代码

class Solution {
public:
    bool isValid(string s) {
        int len = s.size();
        if(len == 0) return false;
        
        stack<char> Stack;
        for(int i = 0; i < len; ++i){
            if(s[i] == '(' || s[i] == '{' || s[i] == '[')
                Stack.push(s[i]);
            else if(s[i] == ')'){
                if(Stack.empty() || Stack.top() != '(')
                    return false;
                else Stack.pop();
            }
            else if(s[i] == '}'){
                if(Stack.empty() || Stack.top() != '{')
                    return false;
                else Stack.pop();
            }
            else if(s[i] == ']'){
                if(Stack.empty() || Stack.top() != '[')
                    return false;
                else Stack.pop();
            }
            else return false;
        }
        
        return Stack.empty();
        
    }
};