[Leetcode] Sudoku solver (iteration)

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.

 

Method: the key to solving this problem is to try it one by one in the alternative set. Not every space can start with a unique fixed number.

class Solution {public:    void solveSudoku(vector<vector<char> > &board) {        vector<set<char>> rowMap(9);        vector<set<char>> colMap(9);        vector<set<char>> boxMap(9);        vector<pair<int,int>> blank;        for(int i=0;i<9;i++)        {            for(int j=0;j<9;j++)            {                if(board[i][j]==‘.‘)                {                    blank.push_back(pair<int,int>(i,j));                    continue;                }                rowMap[i].insert(board[i][j]);            }        }        for(int j=0;j<9;j++)        {            for(int i=0;i<9;i++)            {                if(board[i][j]==‘.‘)                    continue;                colMap[j].insert(board[i][j]);            }        }        for(int i=0;i<9;i=i+3)        {            for(int j=0;j<9;j=j+3)            {                vector<int> mp(10,0);                for(int k=0;k<3;k++)                {                    for(int m=0;m<3;m++)                    {                        if(board[i+k][j+m]==‘.‘)                            continue;                        boxMap[(i/3) * 3 +j/3].insert(board[i+k][j+m]);                    }                }            }        }        found = false;        DFS(0,blank,rowMap,colMap,boxMap,board);    }private:    void DFS(int t, vector<pair<int,int>> &blank,  vector<set<char>> &rowMap,  vector<set<char>> &colMap,  vector<set<char>> &boxMap, vector<vector<char> > &board)    {        if(t>=blank.size())        {            found = true;        }        else        {            int i= blank[t].first;            int j= blank[t].second;            for(char digit =‘1‘;digit<=‘9‘;digit++)            {                if(rowMap[i].count(digit)>0 || colMap[j].count(digit)>0 || boxMap[i/3 * 3 + j/3].count(digit)>0)                {                    continue;                }                board[i][j]=digit;                rowMap[i].insert(digit);                colMap[j].insert(digit);                boxMap[i/3*3+j/3].insert(digit);                DFS(t+1,blank,rowMap,colMap,boxMap,board);                rowMap[i].erase(digit);                colMap[j].erase(digit);                boxMap[i/3*3+j/3].erase(digit);                if(found)                    return;            }        }    }private:    bool found;};

 

 

[Leetcode] Sudoku solver (iteration)