Solution.java

package valid_parentheses;

import java.util.Stack;

class Solution {
    public boolean isValid(String s) {

        Stack<Character> stack = new Stack<>();
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == '(' || s.charAt(i) == '{' || s.charAt(i) == '[') {
                stack.push(s.charAt(i));
            } else {
                if (s.charAt(i) == ')') {
                    if (stack.size() == 0 || stack.pop() != '(') {
                        return false;
                    }
                } else if (s.charAt(i) == '}') {
                    if (stack.size() == 0 || stack.pop() != '{') {
                        return false;
                    }
                } else if (s.charAt(i) == ']') {
                    if (stack.size() == 0 || stack.pop() != '[') {
                        return false;
                    }
                }
            }
        }
        return stack.size() == 0;
    }

}