Hello LeetCode Community! 👋

I recently went through an exciting onsite interview experience with IBM for the Software Development Engineer II (SDE2) position. Today, I'd like to share my journey, particularly how I tackled the classic "N-Queens" problem. This challenge assesses your problem-solving skills and ability to implement an efficient solution.

Interview Details:

• Company: IBM
• Position: Software Development Engineer II (SDE2)
• Interview Type: Onsite
• Question Name: N-Queens Problem

Problem Statement:
Given an integer 'n', return all distinct solutions to the 'n'-queens puzzle. You are required to place 'n' queens on an 'n x n' chessboard, ensuring that no two queens threaten each other.

Example:
For 'n = 4', there are two distinct solutions.

Solution 1:
[".Q..",
 "...Q",
 "Q...",
 "..Q."]

Solution 2:
["..Q.",
 "Q...",
 "...Q",
 ".Q.."]

Code:
Here's my Python solution to the N-Queens problem:

class Solution:
    def solveNQueens(self, n: int) -> List[List[str]]:
        if n == 0:
            return []

        def bt(r):
            if r == n:
                result.append(op[:])
            
            for c in range(n):
                if c in col or r+c in dig or r-c in adig:
                    continue
                col.add(c)
                dig.add(r+c)
                adig.add(r-c)
                op.append('.'*c+'Q'+'.'*(n-c-1))
                bt(r+1)
                col.remove(c)
                dig.remove(r+c)
                adig.remove(r-c)
                op.pop()

        col, dig, adig, op, result = set(), set(), set(), [], []
        bt(0)

        return result

Main Discussion:
During the interview, I began by explaining my thought process before delving into the code. I opted for a backtracking approach to solve the N-Queens problem. This method explores all possible placements of queens on the chessboard, ensuring no two queens threaten each other. By employing backtracking, we efficiently explore all solutions without redundancies.

I encourage fellow candidates preparing for IBM interviews to share their experiences, alternative solutions, or any additional insights into the N-Queens problem. Let's build a helpful resource for the LeetCode community. Remember to format your code using three backticks (```) for clarity, and include diverse examples to illustrate your solutions effectively!

Wishing everyone the best in their interview preparations, and happy coding! 🚀✨ #NQueensProblem

Warm regards,

Vignesh