【LeetCode】020. 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.

 

题解：

　　括号匹配问题，与出现顺序有关，联想到栈和队列。

Solution 1

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