I've got this one. Yahoo! The OA was done through CodeSignal and was 90 minutes in total, consisting of 4 programming questions + a few simple logic/math trivia questions. Overall, I felt that the questions were close to data processing, string processing and basic algorithms, which is not very specialized, but time allocation is the key.
Before starting, the system will give you a simple environment test page, so you can familiarize yourself with the IDE interface and input/output formats in advance. After the official timing, the questions are arranged directly according to the increasing difficulty, the first two questions are more points, and the next two questions need a little more thinking.
Examples of real questions
1. String Compression
Given a string, compress it by replacing consecutive repeating characters with the character followed by the number of repetitions.
Example. "aaabbc" → "a3b2c1"
2. Rotate 2D Matrix
Given an n x n matrix, rotate it 90 degrees clockwise in place.
Example.
[[1,2,3],
[4,5,6],
[7,8,9]]
[[7,4,1],
[8,5,2],
[9,6,3]]
3. Valid Parentheses with Wildcard
Given a string containing (, ), and *, determine if it could be a valid parentheses string.
* can be treated as ( or ) or an empty string.
4. Minimum Path Sum
Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path. you can only move You can only move right or down.
Lessons learned
- The first two questions are mostly giveaways, so try to get them done in 10 minutes.
- Third question to note
*The multiple possibilities of the commonly used interval greed Solution. - The fourth question is a typical dynamic programming, and you can't go wrong if you handle the boundaries well.
- CodeSignal's hidden case coverage is very comprehensive, so special consideration should be given to boundary scenarios such as null inputs, all-zero matrices, and single rows and columns.
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