谷歌的技术面试不仅考察编程能力，还注重对问题的深度理解、分析能力和解决问题的思路。在这次的面试中，面试官提出了一个关于日期验证的题目，候选人需要判断给定的三个数字是否能构成一个有效日期，并且确定该日期是否有多种组合方式。通过还原面试现场的对话，展示如何通过讨论和不断优化来最终达成有效的解决方案。
Google's technical interviews are known for testing not only your coding skills but also your ability to deeply understand, analyze, and problem-solve. In this interview, the problem posed was about validating dates given three numbers and determining if the date is ambiguous (meaning it could be represented in multiple valid ways). This blog post aims to recreate the interview conversation, detailing how discussion and iterative thinking helped reach an optimized solution.
面试开始
面试官：今天的题目是关于日期的验证。我会给你三个数字，你需要判断它们是否能够构成一个有效的日期。值得注意的是，每个数字都有可能代表年份、月份或日期，你需要考虑所有可能的组合，判断日期是否有效。如果是有效日期，还需要判断这个日期是否有多种组合方式可以构成。你有任何问题吗？
候选人：我明白了。这意味着我需要处理所有可能的数字排列组合，对吗？如果多个组合能构成有效日期，我就返回“二义性”；如果只有一种组合，我就返回“唯一性”。
面试官：没错。你会返回两个布尔值：第一个表示日期是否有效，第二个表示日期是否具有二义性。如果没有有效的组合，你就返回无效。
Interview Start
Interviewer: Today's problem is about validating dates. I will give you three numbers, and your task is to determine if they can form a valid date. The twist is that any of the numbers could represent the year, month, or day, so you'll need to consider all possible combinations. Additionally, if there are multiple valid ways to form a date, you'll need to indicate that it's ambiguous. If there’s only one valid combination, you'll mark it as unambiguous. Any questions before we start?
Candidate: Got it. So, I need to handle all possible permutations of the numbers and check each combination, right? If more than one combination forms a valid date, I should mark it as ambiguous, and if there's only one valid combination, it's unambiguous.
Interviewer: Exactly. You'll return two booleans: one indicating whether the numbers can form a valid date and the other indicating whether that date is ambiguous or not. If there's no valid date, you'd return false for both.
初步分析与思路
候选人：好的。我觉得解决这个问题的关键在于生成这三个数字的所有排列组合，然后逐一判断每个组合是否能构成有效日期。我可以通过定义一个辅助函数来计算每个月的天数，特别是要考虑闰年的情况。如果一个组合能够通过验证，那就是有效日期。如果我们发现有多个组合能够构成有效日期，那就说明这个日期具有二义性。
面试官：那你打算如何处理闰年问题呢？
候选人：闰年的规则是，年份能够被4整除，但不能被100整除，除非还能被400整除。我会使用这个规则来判断某个年份是否是闰年。如果是闰年，那么2月的天数是29天，否则是28天。
Initial Analysis and Approach
Candidate: Okay. I think the key to solving this problem is generating all permutations of the three numbers and then validating each combination to see if they can form a valid date. I can write a helper function to check the number of days in each month, especially taking leap years into account. If a permutation passes the validation, it counts as a valid date. If we find more than one valid combination, the date is ambiguous.
Interviewer: How would you handle leap years in this context?
Candidate: A leap year occurs when the year is divisible by 4, but not by 100 unless it's also divisible by 400. I'll use that rule to check if a year is a leap year. If it is, February will have 29 days; otherwise, it will have 28.
逐步解决问题
候选人：我首先会生成三个数字的所有排列组合。因为只有三个数字，组合的数量不会太多，所以我可以通过回溯或者递归来实现。
面试官：那接下来呢？
候选人：对于每个排列组合，我会依次尝试把其中一个数字当作年份，另外两个数字作为月份和日期。我会验证这个组合是否是有效日期。具体来说，我会检查年份是否有效，月份是否在1到12的范围内，日期是否在该月份的最大天数范围内。如果能够满足这些条件，我就认为这是一个有效日期。
Iterative Problem Solving
Candidate: First, I'll generate all permutations of the three numbers since there are only three, meaning a maximum of six permutations. I'll then evaluate each one by treating one number as the year, one as the month, and one as the day.
Interviewer: And after generating the permutations?
Candidate: For each permutation, I'll check whether the combination forms a valid date. Specifically, I'll verify if the year is positive, the month falls within the range of 1 to 12, and the day fits within the valid range of days for that month and year. If the combination satisfies these conditions, I’ll mark it as a valid date.
处理二义性的问题
面试官：那你如何判断这个日期是否具有二义性呢？
候选人：很简单。如果我发现有多个组合都能够构成有效日期，我就认为这个日期是二义性的；如果只有一个组合有效，那么它就是唯一的。如果没有任何组合能构成有效日期，那这个输入就是无效的。
面试官：听起来是个不错的思路。接下来你可以考虑一些边界情况吗？比如月份大于12，或者年份是负数的情况。
候选人：当然，我会确保月份在1到12的范围内，年份必须是正数。此外，我还会考虑闰年情况，如果2月的日期是29天，但年份不是闰年，我会将其判定为无效。
Google Interview Experience: Date Validation and Ambiguity
Google's technical interviews are known for testing not only your coding skills but also your ability to deeply understand, analyze, and problem-solve. In this interview, the problem posed was about validating dates given three numbers and determining if the date is ambiguous (meaning it could be represented in multiple valid ways). This blog post aims to recreate the interview conversation, detailing how discussion and iterative thinking helped reach an optimized solution.
Interview Start
Interviewer: Today's problem is about validating dates. I will give you three numbers, and your task is to determine if they can form a valid date. The twist is that any of the numbers could represent the year, month, or day, so you'll need to consider all possible combinations. Additionally, if there are multiple valid ways to form a date, you'll need to indicate that it's ambiguous. If there’s only one valid combination, you'll mark it as unambiguous. Any questions before we start?
Candidate: Got it. So, I need to handle all possible permutations of the numbers and check each combination, right? If more than one combination forms a valid date, I should mark it as ambiguous, and if there's only one valid combination, it's unambiguous.
Interviewer: Exactly. You'll return two booleans: one indicating whether the numbers can form a valid date and the other indicating whether that date is ambiguous or not. If there's no valid date, you'd return false for both.
Initial Analysis and Approach
Candidate: Okay. I think the key to solving this problem is generating all permutations of the three numbers and then validating each combination to see if they can form a valid date. I can write a helper function to check the number of days in each month, especially taking leap years into account. If a permutation passes the validation, it counts as a valid date. If we find more than one valid combination, the date is ambiguous.
Interviewer: How would you handle leap years in this context?
Candidate: A leap year occurs when the year is divisible by 4, but not by 100 unless it's also divisible by 400. I'll use that rule to check if a year is a leap year. If it is, February will have 29 days; otherwise, it will have 28.
Iterative Problem Solving
Candidate: First, I'll generate all permutations of the three numbers since there are only three, meaning a maximum of six permutations. I'll then evaluate each one by treating one number as the year, one as the month, and one as the day.
Interviewer: And after generating the permutations?
Candidate: For each permutation, I'll check whether the combination forms a valid date. Specifically, I'll verify if the year is positive, the month falls within the range of 1 to 12, and the day fits within the valid range of days for that month and year. If the combination satisfies these conditions, I’ll mark it as a valid date.
Handling Ambiguity
Interviewer: How would you determine whether the date is ambiguous?
Candidate: If more than one permutation results in a valid date, I’ll mark the date as ambiguous. If only one permutation is valid, it’s unambiguous. If none of the permutations are valid, the date will be marked as invalid.
Interviewer: That makes sense. Now, could you consider some edge cases? For instance, what happens if one of the numbers is greater than 12, or if the year is negative?
Candidate: Absolutely. I'll ensure that the month is between 1 and 12, and the year is non-negative. Also, I’ll handle edge cases such as February having 29 days in leap years but only 28 days in non-leap years.
测试边界情况
面试官：你能提供一些测试用例来验证你的想法吗？
候选人：我想出了一些测试用例。比如，输入[2000, 14, 3]，其中14不可能是有效的月份，这个组合应该返回无效。同样，如果输入[2000, 3, 2000]，这个组合也无法形成有效日期，结果应该是无效。再比如输入[2000, 3, 4]，3和4可以互换，既可以作为月和日，也可以作为日和月，因此这个输入应该返回有效且二义性。
Testing Edge Cases
Interviewer: Can you come up with some test cases to validate your approach?
Candidate: Sure. Let’s consider the input [2000, 14, 3]. Since 14 cannot be a valid month, this combination should return false for validity. Another case could be [2000, 3, 2000], which similarly won’t form a valid date, so it should also return false. For [2000, 3, 4], both 3 and 4 could be swapped as month and day, meaning this input is valid and ambiguous.
最后的提问环节
候选人：感谢这次面试，我对这个职位有一些问题。能否告诉我团队的结构是怎样的？我们通常会和多少个开发团队一起协作呢？
面试官：我们有多个跨职能的团队，每个团队专注于不同的产品模块。我们之间有定期的协作，以确保各个产品部分能够很好地集成在一起。
候选人：如果我有幸加入这个团队，入职的流程是怎样的呢？
面试官：你会参加一个为期几天的入职培训，了解我们的技术栈、代码库和产品背景。我们会安排一位经验丰富的工程师担任你的导师，帮助你熟悉开发流程。
候选人：非常感谢，我对加入谷歌更加期待了！
面试官：很高兴与你交流，祝你一切顺利！
Closing with Follow-Up Questions
Candidate: Thank you for this opportunity. I do have a few questions about the role. Could you tell me more about the team structure? How many teams do we typically collaborate with?
Interviewer: We work in cross-functional teams, each focused on different product modules. Regular collaboration ensures that different parts of the product integrate smoothly.
Candidate: And if I were to join the team, what does the onboarding process look like?
Interviewer: You’d go through an onboarding process that lasts a few days, covering our tech stack, codebase, and product background. You’d also be assigned a mentor who will guide you through the development process.
Candidate: That sounds great. Thank you for the information—I’m even more excited about the opportunity to join Google!
Interviewer: It was great speaking with you, and best of luck in the process!
总结
通过这次面试，我们见证了候选人如何面对复杂的日期验证问题，从最初的思路到不断优化，并通过面试官的反馈调整解决方案。谷歌的面试不仅考察编码能力，更考察候选人如何清晰地思考和解释自己的解题思路。希望这篇分享能够帮助大家更好地准备谷歌的面试。
Summary
In this interview, we followed the candidate’s approach to solving a complex date validation problem, from initial analysis through edge case handling and final testing. Google’s interviews challenge not only your technical coding ability but also your logical reasoning and clear communication of your thought process. We hope this post provides insights into how to prepare for a Google interview and tackle such thought-provoking problems.
如果您需要面试辅助或面试代面服务，帮助您进入梦想中的大厂，请随时联系我。
In this Google interview, I demonstrated my understanding of common algorithmic problems and my problem-solving abilities. Each problem presented different challenges, but all could be solved through logical algorithm strategies.
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