20. Valid Parentheses

https://leetcode.com/problems/valid-parentheses/

Problem

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.

2. Open brackets must be closed in the correct order.

Example 1:

Input: s = "()"
Output: true

Example 2:

Input: s = "()[]{}"
Output: true

Example 3:

Input: s = "(]"
Output: false

Example 4:

Input: s = "([)]"
Output: false

Example 5:

Input: s = "{[]}"
Output: true

Constraints:

• 1 <= s.length <= 104

• s consists of parentheses only '()[]{}'.

Solution

class Solution {
public:
    bool isValid(string s) {
        stack<char> stack;
        for (const auto &c: s) {
            if (!closed(c)) {
                stack.push(c);
            } else {
                if (stack.empty() || stack.top() != getPair(c)) return false;
                stack.pop();
            }
        }
        return stack.empty();
    }
    inline char getPair(char c) {
        switch (c) {
            case ')':
                return '(';
            case ']':
                return '[';
            default: // '}'
                return '{';
        }
    }
    inline bool closed(char c) {
        return c == ')' || c == ']' || c =='}';
    }
};

• #stack