1.3.4 判断括号配对

public static boolean parentheses(String s){
    LinkedStack<Character> stack = new LinkedStack<>();
    for(int i = 0; i < s.length(); i++){
        switch(s.charAt(i)){
        case '(': stack.push('('); break;
        case '[': stack.push('['); break;
        case '{': stack.push('{'); break;
        case ')': if(stack.pop() != '(') return false; break;
        case ']': if(stack.pop() != '[') return false; break;
        case '}': if(stack.pop() != '{') return false; break;
        }
    }
    return stack.isEmpty();
}