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3,187 lead backend developer interview questions shared by candidates

Behavioral Why outreach The impact you hope to have from your next role?What is most important factor in your career/job What do you think about RSpec? How do you compare it with other frameworks What was the hardest/Challenging technical problem you faced and how did you resolve it Coding This problem concerns finding a time when we can do daily recurring maintenance on a server. You are to write a function that is given the following information: List of times when the server is busy every day Duration, in minutes, of the desired maintenance window The function should return the start time of a daily maintenance window when the server is not busy. In pseudo-code, the function signature would look something like this: maintWindowStart(busyTimes, durationMins) -> startTime The "busy times" should be time ranges like the following, and can be represented in whatever data structure you feel is appropriate. 0:05 to 0:30 = [5, 30] 2:00 to 4:01 = [120, 241] 13:10 to 16:55 = [790, 1015] [[5, 30], [120, 541], [790, 1015]] // requested duration -> expected start time // 10 -> 30 // 120 -> 541 // 4 -> 0 // 300 -> 1015
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Senior Backend Software Engineer

Interviewed at Outreach

3.8★
Jan 12, 2018

Behavioral Why outreach The impact you hope to have from your next role?What is most important factor in your career/job What do you think about RSpec? How do you compare it with other frameworks What was the hardest/Challenging technical problem you faced and how did you resolve it Coding This problem concerns finding a time when we can do daily recurring maintenance on a server. You are to write a function that is given the following information: List of times when the server is busy every day Duration, in minutes, of the desired maintenance window The function should return the start time of a daily maintenance window when the server is not busy. In pseudo-code, the function signature would look something like this: maintWindowStart(busyTimes, durationMins) -> startTime The "busy times" should be time ranges like the following, and can be represented in whatever data structure you feel is appropriate. 0:05 to 0:30 = [5, 30] 2:00 to 4:01 = [120, 241] 13:10 to 16:55 = [790, 1015] [[5, 30], [120, 541], [790, 1015]] // requested duration -> expected start time // 10 -> 30 // 120 -> 541 // 4 -> 0 // 300 -> 1015

Given an integer, re-arrange the integer such that first and last digit will be at first and second, second and second last digit will be at third and fourth position from left of the re-arranges integer and so on. Example: Input -> 12345678, Output -> 18273645 Input -> 1234567, Output -> 1726354
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Software Engineer, Backend

Interviewed at Zalando

3.6★
Jan 9, 2019

Given an integer, re-arrange the integer such that first and last digit will be at first and second, second and second last digit will be at third and fourth position from left of the re-arranges integer and so on. Example: Input -> 12345678, Output -> 18273645 Input -> 1234567, Output -> 1726354

/* * Your previous Plain Text content is preserved below: * * # Step 1 Throughout this interview, we'll pretend we're building a new * analytical database. Don't worry about actually building a database though – * these will all be toy problems. * * Here's how the database works: all records are represented as maps, with * string keys and integer values. The records are contained in an array, in no * particular order. * * To begin with, the database will support just one function: min_by_key. This * function scans the array of records and returns the record that has the * minimum value for a specified key. Records that do not contain the specified * key are considered to have value 0 for the key. Note that keys may map to * negative values! * * Here's an example use case: each of your records contains data about a school * student. You can use min_by_key to answer questions such as "who is the * youngest student?" and "who is the student with the lowest grade-point * average?" * * Implementation notes: You should handle an empty array of records in an * idiomatic way in your language of choice. If several records share the same * minimum value for the chosen key, you may return any of them. * * ### Java function signature: ``` public static Map<String, Integer> * minByKey(String key, List<Map<String, Integer>> records); ``` * * ### Examples (in Python): ``` assert min_by_key("a", [{"a": 1, "b": 2}, {"a": * 2}]) == {"a": 1, "b": 2} assert min_by_key("a", [{"a": 2}, {"a": 1, "b": 2}]) * == {"a": 1, "b": 2} assert min_by_key("b", [{"a": 1, "b": 2}, {"a": 2}]) == * {"a": 2} assert min_by_key("a", [{}]) == {} assert min_by_key("b", [{"a": * -1}, {"b": -1}]) == {"b": -1} ``` */
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Backend/API Engineer

Interviewed at Stripe

3.7★
May 8, 2019

/* * Your previous Plain Text content is preserved below: * * # Step 1 Throughout this interview, we'll pretend we're building a new * analytical database. Don't worry about actually building a database though – * these will all be toy problems. * * Here's how the database works: all records are represented as maps, with * string keys and integer values. The records are contained in an array, in no * particular order. * * To begin with, the database will support just one function: min_by_key. This * function scans the array of records and returns the record that has the * minimum value for a specified key. Records that do not contain the specified * key are considered to have value 0 for the key. Note that keys may map to * negative values! * * Here's an example use case: each of your records contains data about a school * student. You can use min_by_key to answer questions such as "who is the * youngest student?" and "who is the student with the lowest grade-point * average?" * * Implementation notes: You should handle an empty array of records in an * idiomatic way in your language of choice. If several records share the same * minimum value for the chosen key, you may return any of them. * * ### Java function signature: ``` public static Map<String, Integer> * minByKey(String key, List<Map<String, Integer>> records); ``` * * ### Examples (in Python): ``` assert min_by_key("a", [{"a": 1, "b": 2}, {"a": * 2}]) == {"a": 1, "b": 2} assert min_by_key("a", [{"a": 2}, {"a": 1, "b": 2}]) * == {"a": 1, "b": 2} assert min_by_key("b", [{"a": 1, "b": 2}, {"a": 2}]) == * {"a": 2} assert min_by_key("a", [{}]) == {} assert min_by_key("b", [{"a": * -1}, {"b": -1}]) == {"b": -1} ``` */

Given an array with n integers, check if it could become non-decreasing by removing at most 1 element. Example: Input: [3,2,4,3], Output: false Input:[1, 4, 2, 3], Output: true Input:[4, 3, 2], Output: false Input:[1, 2, 3], Output: true
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Software Engineer, Backend

Interviewed at Zalando

3.6★
Jan 9, 2019

Given an array with n integers, check if it could become non-decreasing by removing at most 1 element. Example: Input: [3,2,4,3], Output: false Input:[1, 4, 2, 3], Output: true Input:[4, 3, 2], Output: false Input:[1, 2, 3], Output: true

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