Sudoku_Solver.cpp

#include <iostream>
#include <vector>

using namespace std;

bool isSafe(vector<vector<int>>& board, int row, int col, int num) {
    for (int i = 0; i < 9; ++i) {
        if (board[row][i] == num || board[i][col] == num) {
            return false;
        }
    }
    
    int startRow = row - row % 3;
    int startCol = col - col % 3;
    
    for (int i = 0; i < 3; ++i) {
        for (int j = 0; j < 3; ++j) {
            if (board[startRow + i][startCol + j] == num) {
                return false;
            }
        }
    }
    
    return true;
}

bool solveSudoku(vector<vector<int>>& board) {
    for (int row = 0; row < 9; ++row) {
        for (int col = 0; col < 9; ++col) {
            if (board[row][col] == 0) {
                for (int num = 1; num <= 9; ++num) {
                    if (isSafe(board, row, col, num)) {
                        board[row][col] = num;
                        if (solveSudoku(board)) {
                            return true;
                        }
                        board[row][col] = 0;
                    }
                }
                return false;
            }
        }
    }
    return true;
}

int main() {
    vector<vector<int>> board = {
        {5, 3, 0, 0, 7, 0, 0, 0, 0},
        {6, 0, 0, 1, 9, 5, 0, 0, 0},
        {0, 9, 8, 0, 0, 0, 0, 6, 0},
        {8, 0, 0, 0, 6, 0, 0, 0, 3},
        {4, 0, 0, 8, 0, 3, 0, 0, 1},
        {7, 0, 0, 0, 2, 0, 0, 0, 6},
        {0, 6, 0, 0, 0, 0, 2, 8, 0},
        {0, 0, 0, 4, 1, 9, 0, 0, 5},
        {0, 0, 0, 0, 8, 0, 0, 7, 9}
    };

    if (solveSudoku(board)) {
        for (int i = 0; i < 9; ++i) {
            for (int j = 0; j < 9; ++j) {
                cout << board[i][j] << " ";
            }
            cout << endl;
        }
    } else {
        cout << "No solution exists." << endl;
    }

    return 0;
}