leetcode-20-valid parentheses

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.

给定一个字符串，判断它是否是一个合法的括号组。

经典的栈匹配的问题。仔细即可。

class Solution {
public:
    bool isValid(string s) {
        stack<char>st;
        for(int i = 0; i < s.length(); i ++)
        {
            switch(s[i]){
                case '(':
                case '[':
                case '{': st.push(s[i]);break;
                case ')': 
                    if(st.empty()) return false;
                    if(st.top()!='(') return false;
                    else st.pop();
                    break;
                case '}':
                    if(st.empty()) return false;
                    if(st.top()!='{') return false;
                    else st.pop();
                    break;
                case ']':
                    if(st.empty()) return false;
                    if(st.top()!='[') return false;
                    else st.pop();
                    break;
                default: continue;
            }
        }
        return st.empty();
    }
};