本周的Tik Tok的OA 2,3题基本送分，第二题选A，第一题比较难，下面分析一下较难的几道题

1. Resource Allocation Matrix

A supercomputing facility uses a highly efficient operating system for various intensive computations ranging from weather prediction to drug discovery. The system is designed to handle many tasks that require a fixed set of resources - R1, R2, R3, and R4. A recent increase in computational demand led to a deadlock in the system. The current state of the system's resource allocation matrix is shown:

Process	Allocation R1	Allocation R2	Allocation R3	Allocation R4	Max R1	Max R2	Max R3	Max R4
P1	0	0	1	2	0	0	1	2
...	...	...	...	...	...	...	...	...

The total number of instances of each resource type is 5.

Based on the information provided, what is the state of the system?

Options:

• The system is in a safe state and can satisfy requests from all processes.
• The system is in an unsafe state and cannot satisfy requests from all processes.
• The system is in a deadlock state with no possibility of progress.
• The system's state cannot be determined from the information given.

分析: 从所给的资源分配矩阵中，我们需要确定系统是否处于安全状态。为此，我们首先计算系统中每种资源的剩余数量，然后检查是否所有进程的最大需求都能得到满足。

假设所有进程突然都要求其最大资源，如果系统能满足任一进程的最大需求，我们就分配所需的资源给该进程。该进程运行完毕后，释放所有资源。这样，我们检查剩下的进程是否也能得到资源满足。如果所有进程都能按此方法得到满足，那么系统就是处于安全状态。

根据提供的数据，我们可以发现在考虑所有进程的最大需求时，系统资源是足够的。因此，系统处于安全状态。

第一题应当选A

4.Channel Rating

Background: The data analysts at ByteDance are analysing some popular channels on Xigua Video. A channel has a collection of n videos, where the number of views of the i-th video is represented by the array element views[i].

Algorithm Description: The data analysts have built an algorithm that calculates the rating of the channel in the following way:

• The rating of the channel is the number of special subarrays of the array views of length at least 3 such that the bitwise XOR of the first and last elements of the subarray is equal to the bitwise XOR of all the other elements within the subarray.

Note: A subarray is a contiguous sequence of elements within an array.

Task: Given a channel with n videos and an array views, find the rating assigned to the channel. Since the answer can be large, return it modulo (10^9 + 7).

Example: Given n = 4 and views = [0, 3, 6, 5]. All the subarrays of length greater than or equal to 3 are explained below:

Subarray	XOR of Border	XOR of Non-Border	Is Special?
[0, 3, 6]	(0 xor 6) = 6	3	No
[3, 6, 5]	(3 xor 5) = 6	6	Yes
[0, 3, 6, 5]	(0 xor 5) = 5	(3 xor 6) = 5	Yes

Hence, the rating of the channel is 2.

分析: 题目的主要目的是找到一个特殊子序列的总数，该子序列满足以下条件：子序列的第一个和最后一个元素的XOR与子序列中其他元素的XOR之和相等。

为了解决这个问题，我们可以通过以下步骤来解决：

1. 对于每一个可能的子序列，计算第一个和最后一个元素的XOR。
2. 同时，也计算该子序列中其他元素的XOR之和。
3. 比较两个XOR的结果。如果它们相等，则该子序列是特殊的。

伪代码:

本次OA花了40分钟轻松AC，如果有OA代做需求，VO助攻需求，可以联系我