0020 - Valid Parentheses

0020 - Valid Parentheses

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order.

Examples

Input: s = "()" Output: true

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

Input: s = "(]" Output: false

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

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

Constraints:

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

Java Solution

class Solution {
    public boolean isValid(String s) {
        if(s.length() < 2) return false;
        
        Stack<Character> stack = new Stack<>();
        
        for(int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if(c =='(' || c =='[' || c == '{') {
                stack.add(c);
                if(i == s.length()-1) return false;
            } else {
                if(stack.isEmpty()) return false;
                char check;
                check = stack.pop();
                if(c == ')' && check != '(') return false;
                if(c == '}' && check != '{') return false;
                if(c == ']' && check != '[') return false;
            }
        }
        return stack.isEmpty();
    }
}