Sudoku Solver Using Backtracking in DSA Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main idea behind the backtracking algorithm in Sudoku solving?

Backtracking tries to fill the Sudoku board by placing numbers one by one. If a number breaks the rules, it goes back (backtracks) and tries a different number until the board is solved.

beginner

What conditions must be checked before placing a number in a Sudoku cell?

The number must not already appear in the same row, the same column, or the same 3x3 box.

intermediate

Why is backtracking suitable for solving Sudoku puzzles?

Because Sudoku requires trying many possibilities and undoing wrong choices, backtracking efficiently explores all options by trying and undoing moves.

beginner

In the context of Sudoku solving, what does 'backtracking' mean?

It means going back to the previous cell to try a different number when the current choice leads to no solution.

intermediate

What is the role of recursion in the Sudoku backtracking algorithm?

Recursion helps to try filling the next empty cell after placing a number, and if it fails, it returns to try other numbers in previous cells.

Which of these is NOT a rule to check before placing a number in Sudoku?

A Number must be greater than 5

B Number must not be in the same column

C Number must not be in the same 3x3 box

D Number must not be in the same row

Sudoku rules only restrict numbers in rows, columns, and boxes, not their value relative to 5.

What happens if backtracking finds no valid number for a cell?

A It goes back to the previous cell to try a different number

B It moves to the next cell anyway

C It stops and returns failure

D It fills the cell with zero

Backtracking goes back to the previous cell to try other numbers when no valid number fits the current cell.

What data structure is commonly used to represent the Sudoku board in code?

A Linked list

B 2D array

C Stack

D Queue

A 2D array is used to represent the 9x9 Sudoku grid.

Which programming concept allows the Sudoku solver to try filling cells one by one?

A Iteration

B Hashing

C Sorting

D Recursion

Recursion allows the solver to fill one cell and then call itself to fill the next.

What is the base case in the Sudoku backtracking algorithm?

A When the board is empty

B When a cell has no valid number

C When all cells are filled correctly

D When the first cell is filled

The base case is when the entire board is filled without conflicts, meaning the puzzle is solved.

Explain how backtracking helps solve a Sudoku puzzle step-by-step.

Think about trying and undoing moves like exploring paths.

Describe the checks needed before placing a number in a Sudoku cell.

Remember Sudoku rules about unique numbers in rows, columns, and boxes.