Valid Sudoku 和 Sudoku Solver

题目一：Valid Sudoku

Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.

The Sudoku board could be partially filled, where empty cells are filled with the character '.'.

A partially filled sudoku which is valid.

Note:
A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.

思路：循环判断每一行，每一列，每一个方块是否有效

class Solution {public:    bool isValidSudoku(vector<vector<char> > &board) {    vector<bool> check(9,false);    int i,j,block;    for(i = 0;i < 9;++i)//判断每一行是否有效    {    check.assign(9,false);    for(j = 0; j < 9;++j)    {    if(board[i][j] == '.')continue;    if(check[board[i][j] - '0'])return false;    check[board[i][j] - '0'] = true;    }    }    for(i = 0;i < 9;++i)//判断每一列是否有效    {    check.assign(9,false);    for(j = 0;j < 9;++j)    {    if(board[j][i] == '.')continue;    if(check[board[j][i] - '0'])return false;    check[board[j][i] - '0'] = true;    }    }    for(block = 0;block < 9;++block)//判断每一块是否有效    {    int startx = (block/3)*3;//选择每一块的开始位置    int starty = (block%3)*3;    check.assign(9,false);    for(i = startx; i < startx+3;++i)    {    for(j = starty;j < starty+3;++j)    {    if(board[i][j] == '.')continue;    if(check[board[i][j] - '0'])return false;    check[board[i][j] - '0'] = true;    }    }    }    return true;    }};

题目二：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.

思路：递归测试每一个空白点是否有效，和n皇后类似

class Solution {public:    bool check_valid(vector<vector<char> >& board,int row,int col)    {    int i,j;    for(i = 0;i < 9;++i)//判断该行是否有效    {    if(i != col && board[row][i] == board[row][col])return false;    }    for(i = 0;i < 9;++i)//判断该列是否有效    {    if(i != row && board[i][col] == board[row][col])return false;    }    for(i = (row / 3)*3;i < (row /3 +1)*3;++i)//判断该块是否有效    {    for(j = (col / 3)*3;j < (col / 3+1)*3;++j)    {    if(i != row && j != col && board[i][j] == board[row][col])return false;    }    }    return true;    }        bool isValidSudoku(vector<vector<char> >& board)    {    int row,col;    for(row = 0;row < 9;++row)    {    for(col = 0;col < 9;++col)    {    if(board[row][col] == '.')    {    int i;    for(i = 1;i <= 9;++i)//测试每一个数字是否有效    {    board[row][col] = i + '0';    if(check_valid(board,row,col) && isValidSudoku(board))return true;    }    board[row][col] = '.';    return false;    }    }    }    return true;    }    void solveSudoku(vector<vector<char> > &board) {    isValidSudoku(board);    }};