[LeetCode]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.

DFS搜索,加上，回溯法解题。

<span style="font-size:18px;">class Solution {
public:
    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=0 ; k<9; ++k){
                            board[i][j] = '1'+k;
                            if(isValidSudoku(board,i,j)&&solveSudoku(board)){ //走下一步
                                return true;
                            }
                            board[i][j] = '.';//回溯
                    }
                    return false; //没有有效解，该解法返回false
                }
            }
        }
        return true;
    }
    bool isValidSudoku(vector<vector<char> > &board,int x,int y) {  //检查下一步是否合法
      for(int i=0; i<9; ++i){
          if(i!=x && board[i][y] == board[x][y]){
              return false;
          }
      }
      for(int j=0; j<9; ++j){
          if(j!=y && board[x][j] == board[x][y]){
              return false;
          }
      }
      for(int i = 3*(x/3); i<3*(x/3+1); ++i){
          for(int 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;
    }
};</span>