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N-Queens Test | Pre-employment assessment - Testlify
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N-Queens Test

Overview of N-Queens Test

The "n-queens" problem involves placing "n" chess queens on an "n x n" board so they don't threaten each other. backtracking and optimization techniques are used to find solutions. this problem has applications in algorithms, optimization.

Skills measured

  • recursion
  • backtracking

Available in



Coding Test


20 Mins





Use of N-Queens test

The solution approach of "N-Queens" problem is using backtracking. The goal is to find all distinct solutions for placing "N" queens on an "N x N" chessboard without any queen threatening another. The solution utilizes a depth-first search approach to explore possible configurations efficiently.

The function solveNQueens takes an integer n as input and returns a vector of vectors of strings representing the solutions. The backtrack function is used to perform the actual exploration.

In the backtrack function, the algorithm iterates through each column in the current row r. It checks whether placing a queen at the current position is valid, considering the constraints of not sharing the same column or diagonals with other queens. If the position is valid, the queen is placed, and the corresponding flags are updated to mark the occupied columns and diagonals.

The recursion continues to the next row, and the process repeats. When all queens are placed successfully, a valid solution is found and added to the result vector.

If a solution isn't possible in the current configuration, the algorithm backtracks by resetting the board, column, and diagonal flags to their previous state, allowing the algorithm to explore other possibilities.

The solveNQueens function returns a vector containing all solutions, where each solution is represented by a vector of strings, indicating the queen positions on the board.

Relevant for

  • Software Developer Engineer
  • Software Developer
  • Software Engineers

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Recursion is a crucial skill covered in the N-Queens problem, as it allows us to break down the problem into smaller, more manageable subproblems. By defining a recursive function to place queens on the board one by one, we can explore all possible solutions and backtrack when a dead end is reached. This technique is important in solving complex problems efficiently, as it eliminates the need for nested loops and reduces the amount of code required. Recursion also helps in improving the readability and maintainability of the code, making it easier to understand and debug.



Backtracking is a crucial skill covered in the N-Queens problem, as it allows for the efficient exploration of all possible solutions. By systematically trying different arrangements of queens on the chessboard and backtracking when a dead-end is reached, the algorithm can quickly eliminate invalid configurations and focus on finding the correct solution. This approach helps in reducing the time complexity of the problem and ensures that all possible solutions are considered. Overall, mastering the backtracking skill is essential for solving complex problems like N-Queens efficiently and effectively.

The N-Queens test is created by a subject-matter expert

Testlify’s skill tests are designed by experienced SMEs (subject matter experts). We evaluate these experts based on specific metrics such as expertise, capability, and their market reputation. Prior to being published, each skill test is peer-reviewed by other experts and then calibrated based on insights derived from a significant number of test-takers who are well-versed in that skill area. Our inherent feedback systems and built-in algorithms enable our SMEs to refine our tests continually.

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