N Queens Problem in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the chessboard with empty cells represented by '.'

DSA Typescript

const board: string[][] = Array.from({ length: n }, () => Array(n).fill([1]));

Drag options to blanks, or click blank then click option'

A'.'

B'x'

C'Q'

D' '

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Q' instead of '.' to initialize the board.

Using a space ' ' which can be confusing visually.

The board should be initialized with '.' to represent empty cells.

2fill in blank

medium

Complete the code to check if placing a queen at (row, col) is safe by checking the same column.

DSA Typescript

for (let i = 0; i < row; i++) {
  if (board[i][[1]] === 'Q') return false;
}

Drag options to blanks, or click blank then click option'

Ai

B0

Ccol

Drow

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'row' instead of 'col' which checks the wrong column.

Using 'i' which is the row index, not column.

We check the same column 'col' in all previous rows to ensure no queen is placed there.

3fill in blank

hard

Fix the error in the diagonal check to correctly verify the upper left diagonal for a queen.

DSA Typescript

for (let i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--) {
  if (board[i][[1]] === 'Q') return false;
}

Drag options to blanks, or click blank then click option'

Acol

Bi

Crow

Dj

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'i' as column index which is incorrect.

Using fixed 'col' or 'row' instead of loop variable 'j'.

We must check the cell at (i, j) on the upper left diagonal, so use 'j' as the column index.

4fill in blank

hard

Fill both blanks to check the upper right diagonal for a queen safely.

DSA Typescript

for (let i = row - 1, j = col + [1]; i >= 0 && j < n; i--, j[2]) {
  if (board[i][j] === 'Q') return false;
}

Drag options to blanks, or click blank then click option'

A1

B-1

C+= 1

D--

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-1' for initial j which moves left instead of right.

Using '--' which decreases j instead of increasing.

We start at col + 1 and increment j each iteration to move upper right diagonal.

5fill in blank

hard

Fill all three blanks to place a queen, recurse, and then remove the queen (backtrack).

DSA Typescript

board[row][col] = [1];
if (solveNQueens(board, n, row + 1)) return true;
board[row][col] = [2]; // backtrack
return [3];

Drag options to blanks, or click blank then click option'

A'Q'

B'.'

Cfalse

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'true' instead of 'false' in the return statement causing incorrect recursion.

Not resetting the cell to '.' during backtracking.

Place 'Q' to mark queen, backtrack by resetting to '.', and return false if no solution.