LeetCode笔记：37. Sudoku Solver

回溯法解决数独问题：核心代码：

 bool solveSudoku(vector<vector<char>> &board, int i, int j)    {        if(i==9) return true;        if(j==9) return solveSudoku(board, i+1, 0);        if(board[i][j] != '.') return solveSudoku(board, i, j+1);            for(int c=1; c<=9; c++)        {            if(validsodu(board, i, j, c))            {                board[i][j] = c+'0';                if(solveSudoku(board, i, j+1)) return true;                board[i][j] = '.';            }        }                    return false;    }