ValidParentheses.java

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

import java.util.Stack;
class Solution {
    public boolean isValid(String s) {
        Stack<Character> stack=new Stack<Character>();
        //create an empty stack
        for(char c:s.toCharArray()){
            if(c=='(')
                stack.push(')');
            else if(c=='{')
                stack.push('}');
            else if(c=='[')
                stack.push(']');
            
            else if(stack.isEmpty() || stack.pop()!= c)
                return false;
            
        }
         return stack.isEmpty();
    }}