Sudoku Solver (C++)

Overview

This project is a Sudoku Solver implemented in C++ using a classic backtracking algorithm. The program takes predefined 9×9 Sudoku boards, validates their initial state, and attempts to solve them. If a solution exists, the completed board is printed to the console. Otherwise, the program reports that the puzzle cannot be solved.

This project demonstrates:

Recursive backtracking
Constraint checking (row, column, 3×3 box)
Use of vector<vector> for 2D board representation
Basic input validation

Features

・Solves standard 9×9 Sudoku puzzles
・Detects invalid initial boards (duplicate numbers in rows or columns)
・Uses 0 to represent empty cells
・Handles multiple test boards in a single execution
・Clearly reports whether each board is solvable

Algorithm

The solver uses a backtracking approach:

1. Find the next empty cell (value 0)
2. Try numbers from 1 to 9
3. Check if the number is valid:
   ・　Not already in the same row
   ・　Not already in the same column
   ・ Not already in the corresponding 3×3 subgrid
   
4. Recursively attempt to solve the rest of the board
5. If a conflict occurs, reset the cell and backtrack