Kakao Releases 2020 New Graduate Developer First Coding Test Problems and Solutions

Kakao has released the 7 problems and detailed solutions for the first coding test of its 2020 new graduate developer recruitment. The test was conducted on the 7th for 5 hours, allowing candidates to choose one of six languages, including C++, Java, and Python.

The problems were arranged in order of difficulty, and except for Question 4, which includes efficiency tests, all test cases must be passed to be considered correct. The published explanations include the intent behind each problem and optimized algorithmic approaches.

Key Problem Types and Explanations

• String Compression (Q1): A problem that requires finding the shortest compressed length by cutting a string into specific units and representing repeated parts with numbers. Due to the limited input size (1,000 or less), brute force search is possible.
• Parentheses Conversion (Q2): A problem that requires converting a balanced parentheses string into a correct parentheses string according to a given algorithm. Implementation skills using recursive functions are the key evaluation points.
• Lock and Key (Q3): A problem that requires determining whether all grooves of a lock can be filled by rotating and moving a 2D array. It involves exploring all possible cases using array rotation functions.
• Word Search (Q4): A problem that requires searching for words using patterns containing the wildcard '?'. While the correctness solution involves simple comparison, Trie data structures or binary search must be used to pass efficiency tests. Specifically, a method of constructing two Tries by reversing strings to handle prefix/suffix patterns was presented.
• Installing Pillars and Beams (Q5): A problem that requires simulating whether the structure remains valid when pillars and beams are installed or deleted according to rules. The core logic is verifying that the remaining structures satisfy the rules upon deletion.
• Wall Inspection (Q6): A problem that requires inspecting vulnerable points on a circular wall with the minimum number of friends. It utilizes the array rotation technique of unrolling the circle into a straight line and permutations to find the optimal solution.
• Moving on an Uninhabited Island (Q7): A problem that requires finding the minimum time for a 2x1 robot to move to a destination while avoiding walls. BFS is performed by defining the robot's position and direction as a state, and collision detection during rotation must be precisely determined.