Valid Parentheses

Description

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.
3. Every close bracket has a corresponding open bracket of the same type.

Example 1:

Input: s = ”()” Output: true

Example 2:

Input: s = ”()[]{}” Output: true

Example 3:

Input: s = ”(]” Output: false

Constraints:

• 1 <= s.length <= 104
• s consists of parentheses only '()[]{}'.

Code

Stack

Time Complexity: $O(N)$, Space Complexity: $O(N)$

class Solution {
public:
    bool isValid(string s) {
        unordered_map<char, char> mp;
        mp[')'] = '(';
        mp['}'] = '{';
        mp[']'] = '[';
        stack<char> st;
        for(auto c: s) {
            if(c == '(' || c == '{' || c == '[') st.push(c);
            else {
                if(st.empty() || st.top() != mp[c]) return false;
                st.pop();
            }
        }
        return st.empty();
    }
};

Source

• Valid Parentheses - LeetCode