题解 | #有效括号序列#

class Solution {
public:
    
    bool isValid(string s) {
        stack<char> st;//栈
        int len=s.size();
        for(int i=0;i<len;i++){//遍历字符串
            if(s[i]=='('||s[i]=='['||s[i]=='{'){//左括号入栈
                st.push(s[i]);
            }else if(s[i]==')'){//分别判断右括号
                if(!st.empty()&&st.top()=='('){//如果括号不匹配或者栈为空，则返回失败
                    st.pop();
                }else{
                    return false;
                }
            }else if(s[i]==']'){
                if(!st.empty()&&st.top()=='['){
                    st.pop();
                }else{
                    return false;
                }
            }else if(!st.empty()&&s[i]=='}'){
                if(st.top()=='{'){
                    st.pop();
                }else{
                    return false;
                }
            }
        }
        if(st.size()!=0)//最后如果栈还存在左括号，则返回失败
            return false;
        return true;
    }
};