30. 包含 min 函数的栈#

private Stack<Integer> dataStack = new Stack<>();
private Stack<Integer> minStack = new Stack<>();

public void push(int node) {
    dataStack.push(node);
    minStack.push(minStack.isEmpty() ? node : Math.min(minStack.peek(), node));
}

public void pop() {
    dataStack.pop();
    minStack.pop();
}

public int top() {
    return dataStack.peek();
}

public int min() {
    return minStack.peek();
}