Sudoku Solver Using Backtracking in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a number is already in the given row.

DSA Typescript

function isInRow(board: number[][], row: number, num: number): boolean {
  for (let col = 0; col < 9; col++) {
    if (board[row][col] === [1]) {
      return true;
    }
  }
  return false;
}

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

Acol

Brow

Cnum

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with row or col instead of num.

Using assignment '=' instead of comparison '==='.

We compare each cell in the row with the number we want to place. If any cell equals num, return true.

2fill in blank

medium

Complete the code to check if a number is already in the given column.

DSA Typescript

function isInCol(board: number[][], col: number, num: number): boolean {
  for (let row = 0; row < 9; row++) {
    if (board[row][col] === [1]) {
      return true;
    }
  }
  return false;
}

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

Arow

Bcol

C0

Dnum

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with row or col instead of num.

Using assignment '=' instead of comparison '==='.

We check each cell in the column to see if it equals the number we want to place.

3fill in blank

hard

Fix the error in the code to check if a number is in the 3x3 box containing (row, col).

DSA Typescript

function isInBox(board: number[][], row: number, col: number, num: number): boolean {
  const boxStartRow = row - (row % 3);
  const boxStartCol = col - (col % 3);
  for (let r = boxStartRow; r < boxStartRow + 3; r++) {
    for (let c = boxStartCol; c < boxStartCol + 3; c++) {
      if (board[r][c] === [1]) {
        return true;
      }
    }
  }
  return false;
}

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

Anum

B0

Ccol

Drow

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with row or col instead of num.

Using assignment '=' instead of comparison '==='.

We check each cell in the 3x3 box to see if it equals the number we want to place.

4fill in blank

hard

Fill both blanks to complete the function that checks if placing num at (row, col) is valid.

DSA Typescript

function isValid(board: number[][], row: number, col: number, num: number): boolean {
  return !isInRow(board, row, num) && !isInCol(board, col, num) && !isInBox(board, [1], [2], num);
}

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

Arow

Bcol

Cnum

Dboard

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping row and col arguments.

Passing num or board instead of row or col.

We pass the current row and column to isInBox to check the 3x3 box correctly.

5fill in blank

hard

Fill all three blanks to complete the backtracking function that solves the Sudoku board.

DSA Typescript

function solveSudoku(board: number[][]): boolean {
  for (let row = 0; row < 9; row++) {
    for (let col = 0; col < 9; col++) {
      if (board[row][col] === 0) {
        for (let num = 1; num <= 9; num++) {
          if ([1](board, row, col, num)) {
            board[row][col] = num;
            if ([2](board)) {
              return true;
            }
            board[row][col] = [3];
          }
        }
        return false;
      }
    }
  }
  return true;
}

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

AisValid

BsolveSudoku

C0

DisInRow

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong function names in blanks.

Not resetting the cell to 0 after backtracking.

We check if placing num is valid, then recursively try to solve the board. If it fails, reset cell to 0.