Valid Parentheses LeetCode Solution

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 '()[]{}'.

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

Solution using stack #

class Solution { public: bool isValid(string s) { stack st;

    // using stack to solve this problem helps us to respect the relative placement of brackets
    
    for(int i=0;i<s.length();i++) {
        char top = st.empty() ? '#' : st.top();
        
        if(top == '(' && s\[i\] == ')') {
            st.pop();
        }else if(top == '{' && s\[i\] == '}') {
            st.pop();
        }else if(top == '\[' && s\[i\] == '\]') {
            st.pop();
        }else{
            st.push(s\[i\]);
        }    
    }
    
    return st.empty();
}

};