Sudoku Solver

Write a program to solve a Sudoku puzzle by filling the empty cells.

Empty cells are indicated by the character '.'.

You may assume that there will be only one unique solution.

A sudoku puzzle...

...and its solution numbers marked in red.

和valid sudoku差不多，每行、列、块不能有重复。

DFS+回溯可以解决。

bool isValid(vector<vector<char> > &board, int x, int y){    int i, j;    for (i = 0; i < 9; i++)        if (i != x && board[i][y] == board[x][y])            return false;    for (j = 0; j < 9; j++)        if (j != y && board[x][j] == board[x][y])            return false;    for (i = 3 * (x / 3); i < 3 * (x / 3 + 1); i++)        for (j = 3 * (y / 3); j < 3 * (y / 3 + 1); j++)            if (i != x && j != y && board[i][j] == board[x][y])                return false;    return true;}bool solveSudoku(vector<vector<char> > &board){    for (int i = 0; i < 9; ++i)        for (int j = 0; j < 9; ++j)        {            if (board[i][j]=='.')            {                for (int k = 1; k <= 9; ++k)                {                    board[i][j] = '0' + k;                    if (isValid(board, i, j) && solveSudoku(board))                        return true;                    board[i][j] = '.';                }                return false;            }        }    return true;}