Valid Parenthesis

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 '()[]{}'.
    • 











Solution





Java
class Solution {
    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<Character>();
        for(int i = 0 ; i < s.length(); i++) {
            char ch = s.charAt(i);
            if(ch == '(' || ch == '{' || ch == '[') stack.push(ch);
            else if(ch == ')' || ch == '}' || ch == ']') {
                if(stack.size() == 0) return false;
                char top = stack.pop();
                if(top == '(' && ch != ')') return false;
                else if(top == '{' && ch != '}') return false;
                else if(top == '[' && ch != ']') return false;
            }
        }
        return stack.size() == 0;
    }
}
Agnibha Chandra