N-Queens

LEETCODE PROBLEM SOLVING
PROBLEM->N-QUEENS
import java.util.*;

class Solution {
    List<List<String>> result = new ArrayList<>();
    char[][] board;

    public List<List<String>> solveNQueens(int n) {
        board = new char[n][n];

        for (int i = 0; i < n; i++) {
            Arrays.fill(board[i], '.');
        }

        backtrack(0, n);
        return result;
    }

    private void backtrack(int row, int n) {
        if (row == n) {
            result.add(construct());
            return;
        }

        for (int col = 0; col < n; col++) {
            if (isSafe(row, col, n)) {
                board[row][col] = 'Q'; 

                backtrack(row + 1, n);

                board[row][col] = '.'; 
            }
        }
    }

    private boolean isSafe(int row, int col, int n) {
       
        for (int i = 0; i < row; i++) {
            if (board[i][col] == 'Q') return false;
        }
        for (int i = row - 1, j = col - 1;
             i >= 0 && j >= 0;
             i--, j--) {
            if (board[i][j] == 'Q') return false;
        }
        for (int i = row - 1, j = col + 1;
             i >= 0 && j < n;
             i--, j++) {
            if (board[i][j] == 'Q') return false;
        }

        return true;
    }

    private List<String> construct() {
        List<String> temp = new ArrayList<>();
        for (char[] row : board) {
            temp.add(new String(row));
        }
        return temp;
    }
}