解题思路：

class Solution {
    public boolean validateBookSequences(int[] putIn, int[] takeOut) {
        Stack<Integer> stack = new Stack<>();
        int i = 0;
        for(int num : putIn) {
            stack.push(num); // num 入栈
            while(!stack.isEmpty() && stack.peek() == takeOut[i]) { // 循环判断与出栈
                stack.pop();
                i++;
            }
        }
        return stack.isEmpty();
    }
}