Valid Parentheses

class Solution {
    public boolean isValid(String s) {
        if (s.length() == 1) return false;
        Stack<Character> st = new Stack<>();
        for (int i = 0 ; i < s.length() ; ++i) {
            char c = s.charAt(i);
            if (c == '(' || c == '[' || c == '{') {
                st.push(c);
            }
            else {
                if (st.empty()) return false;
                else if (st.peek() == '(' && c == ')') st.pop();
                else if (st.peek() == '{' && c == '}') st.pop();
                else if (st.peek() == '[' && c == ']') st.pop();
                else return false;
            }
        }
        return st.empty();
    }
}