Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[‘ and ‘]’, determine if the input string is valid.

The brackets must close in the correct order, “()” and “()[]{}” are all valid but “(]” and “([)]” are not.

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public class Solution {
    public boolean isValid(String s) {
        if (s == null || s.length() < 1 || s.length() % 2 == 1){return false;}
        Stack<Character> stack = new Stack<Character>();

        for (int i = 0; i < s.length(); i++) {
            char cur = s.charAt(i);
            if (cur == '{' || cur == '[' || cur == '(') {
                stack.push(cur);
            } else if (cur == '}' && !stack.empty() && stack.peek() == '{') {
                stack.pop();
            } else if (cur == ']' && !stack.empty() && stack.peek() == '[') {
                stack.pop();
            } else if (cur == ')' && !stack.empty() && stack.peek() == '(') {
                stack.pop();
            } else {
                return false;
            }
        }
        return stack.empty();
    }
}