백준 2580번 : 스도쿠

#include <iostream>
#include <vector>
using namespace std;

bool isSafe(const 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 / 3) * 3, startCol = (col / 3) * 3;
    for (int i = startRow; i < startRow + 3; i++) {
        for (int j = startCol; j < startCol + 3; j++) {
            if (board[i][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(9, vector<int>(9));

    for (int i = 0; i < 9; i++) {
        for (int j = 0; j < 9; j++) {
            cin >> board[i][j];
        }
    }

    solveSudoku(board);

    for (int i = 0; i < 9; i++) {
        for (int j = 0; j < 9; j++) {
            cout << board[i][j] << " ";
        }
        cout << endl;
    }

    return 0;
}