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```import java.util.Scanner;

public class NQueensProblem {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);

System.out.print("Enter the number of queens (N): ");
int n = scanner.nextInt();

int[] queens = new int[n];

if (solveNQueens(queens, 0)) {
System.out.println("Solution found:");
printBoard(queens);
} else {
System.out.println("No solution exists.");
}
}

private static boolean solveNQueens(int[] queens, int row) {
if (row == queens.length) {
return true; // All queens are placed successfully
}

for (int col = 0; col < queens.length; col++) {
if (isValid(queens, row, col)) {
queens[row] = col; // Place queen in the current cell

// Recursively solve for the next row
if (solveNQueens(queens, row + 1)) {
return true;
}

// Backtrack if the current placement doesn't lead to a solution
queens[row] = -1;
}
}

return false; // No valid placement for the current row
}

private static boolean isValid(int[] queens, int row, int col) {
// Check if placing a queen in the current cell is valid
for (int i = 0; i < row; i++) {
if (queens[i] == col || queens[i] - i == col - row || queens[i] + i == col + row) {
return false;
}
}

return true;
}

private static void printBoard(int[] queens) {
for (int i = 0; i < queens.length; i++) {
for (int j = 0; j < queens.length; j++) {
if (queens[i] == j) {
System.out.print("Q ");
} else {
System.out.print(". ");
}
}
System.out.println();
}
}
}
```