LeetCode --- Valid Parentheses

题目链接

Problem discription

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.

Accpted Code:

class Solution {
public:
    bool isValid(string s) {
        map<char, char> brackets;
        brackets['{'] = '}';
        brackets['['] = ']';
        brackets['('] = ')';
        // use a stack to store every left brackets
        stack<char> leftBracket;
        // length of s
        int len = (int)s.length();
        
        for (int i = 0; i < len; i++) { 
            if (s[i] == '(' || s[i] == '[' || s[i] == '{') {
                leftBracket.push(s[i]);
            } else {
                // there is no left bracket
                if (leftBracket.empty()) return false;
                char last = leftBracket.top();
                // the previous left bracket doesn't match s[i]
                if (brackets[last] != s[i]) return false;
                leftBracket.pop();
            }
        }
        // if there are some  brackets left 
        // not used(no right brackets to match them)
        return leftBracket.empty();
    }
};