Description

Submission

class Solution {
public:
    bool isValid(vector<vector<char>>& board, int row, int col, char val) {
        for(int i = 0; i < board.size(); ++i) {
            if(board[row][i] == val) return false;
            if(board[i][col] == val) return false;
            int r = row / 3 * 3 + i / 3;
            int c = col / 3 * 3 + i % 3;
            if(board[r][c] == val)
                return false;
        }
        return true;
    }
    
    bool solve(vector<vector<char>>& board) {
        for(int i = 0; i < board.size(); ++i) {
            for(int j = 0; j < board.size(); ++j) {
                if(board[i][j] == '.') {
                    for(int k = 0; k < 9; ++k) {
                        if(isValid(board, i, j, '1' + k)) {
                            board[i][j] = '1' + k;
                            if(solve(board)) return true;
                            board[i][j] = '.';
                        }
                    }
                    return false;
                }
            }
        }
        return true;
    }
    
    void solveSudoku(vector<vector<char>>& board) {
        solve(board);
    }

};

References

1. https://leetcode.com/problems/sudoku-solver/discuss/734304/Extremely-Simple-CPP-Solution-with-excessive-comments-and-Line-by-Line-explanation.