[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.

下面的算法用广度搜索的思想，在每一个空的cell处，找出所有可用的数字，填入一个可用的数字后，把当前的Sudoku的状态入队列。

代码如下：

class Solution {
public:
    bool find(vector<vector<char> > &cur, int &i, int &j){
        for (int ii=0;ii<9;ii++){
            for (int jj=0;jj<9;jj++){
                if (cur[ii][jj]=='.'){
                    i=ii;
                    j=jj;
                    return true;
                }
            }
        }
        return false;
    }
     
    unordered_set<char> valid(int i, int j, vector<vector<char> > &cur){
        unordered_set<char> se({'1','2','3','4','5','6','7','8','9'});
        for (int ii=0;ii<9;ii++){
            se.erase(cur[ii][j]);
            se.erase(cur[i][ii]);
        }
         
        for (int ii=0;ii<3;ii++){
            for (int jj=0;jj<3;jj++){
                se.erase(cur[(i/3)*3+ii][(j/3)*3+jj]);
            }
        }
         
        return se;
         
    }
    void solveSudoku(vector<vector<char> > &board) {
        queue<vector<vector<char> > > que;
        que.push(board);
        vector<vector<char> > cur;
        unordered_set<char> se;
        int i=0;
        int j=0;
        while (!que.empty()){
            cur = que.front();
            que.pop();
            if (find(cur,i,j)==false){
                board = cur;
                return;
            }else{
                se = valid(i,j,cur);
                for (const char& x: se){
                    cur[i][j]=x;
                    que.push(cur);  
                }
            }
        }
    }
};