Leetcode - 20. Valid Parentheses

题目介绍

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.

解法 using stack

bool isValid(string s) {
stack<char> paren;
for (char& c : s) {
switch (c) {
case '(':
case '{':
case '[': paren.push(c); break;
case ')': if (paren.empty() || paren.top()!='(') return false; else paren.pop(); break;
case '}': if (paren.empty() || paren.top()!='{') return false; else paren.pop(); break;
case ']': if (paren.empty() || paren.top()!='[') return false; else paren.pop(); break;
default: ; // pass
}
}
return paren.empty() ;
}