37. Sudoku Solver

Problem

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…

Solution

class Solution {public:    void solveSudoku(vector<vector<char>>& board) {        solveSudokudfs(board);    }    bool solveSudokudfs(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) && solveSudokudfs(board))                              return true;                          //回溯                        board[i][j] = '.';                      }                      return false;                  }              }          return true;      }      bool isValid(vector<vector<char> > &board, int row, int col) {          int i,j;          //查看同一列是否有重复        for(i = 0; i < 9; i++)              if(i != row && board[i][col] == board[row][col])                  return false;          //查看同一行是否有重复        for(j = 0; j < 9; j++)              if(j != col && board[row][j] == board[row][col])                  return false;          //小九宫格内是否有重复, x,y 是小9宫格的左上角的坐标        int x = row/3*3;          int y = col/3*3;          for(i = 0; i < 3; i++)              for(j = 0; j< 3; j++)                  if(x+i != row && y+j != col && board[x+i][y+j] == board[row][col])                      return false;          return true;      }  };