My journey in competitive programming

1. N-Queens II:

Unlike the classic N-Queens problem where we return all valid configurations of the board, in N-Queens II, we are only interested in returning the count of distinct solutions for placing n queens on an n x n chessboard.

Important Points:

1. The constraints and rules are the same: no two queens can threaten each other.
2. Use backtracking to check all valid arrangements row by row.
3. Only count the number of valid configurations, instead of storing all configurations.

2. 3Sum Closest:

For any given integer array nums and any given target, find three integers from nums such that their sum is closest to target. Return the sum of the three integers. You may assume each input would have exactly one solution.

Important Points:

1. This problem is an extension of the 3Sum problem, except here we are not looking for all triplets that sum to zero but for the triplet that is closest to a given target.
2. Sorting the array makes finding triplets less complicated and avoids duplication checks.
3. Use a two-pointer approach for efficiency.