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...

 

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class Solution {public:    bool isValidRow(int row , vector<vector<char> >& board){        vector<int> cnt(10,0);        for(int col = 0; col < 9; ++ col){            char item = board[row][col];            if(item != ‘.‘){                if(cnt[item-‘0‘]!=0) return false;                else cnt[item-‘0‘]++;            }        }        return true;    }        bool isValidCol(int col, vector<vector<char> >& board ){        vector<int> cnt(10,0);        for(int row = 0; row < 9; ++ row){            char item = board[row][col];            if(item != ‘.‘){                if(cnt[item-‘0‘]!=0) return false;                else cnt[item-‘0‘]++;            }        }        return true;    }        bool isValidBox(int i,int j, vector<vector<char> >& board){        vector<int> cnt(10,0);        for(int row = 3*i;row < 3*i+3; ++row){            for(int col = 3*j; col < 3*j+3; ++col){                char item = board[row][col];                if(item != ‘.‘){                    if(cnt[item-‘0‘]!=0) return false;                    else cnt[item-‘0‘]++;                }            }        }        return true;    }    bool isValidSudoku(int x, int y,vector<vector<char> > &board) {        return isValidRow(x,board)&&isValidCol(y,board)&&isValidBox(x/3,y/3,board);    }        bool dfs(int pos ,vector<vector<char> >& board){        int n = board.size();        if(pos == n*n) return true;        int x = pos/n, y = pos%n;        if(board[x][y]==‘.‘){            for(char i = ‘1‘; i<=‘9‘;++ i){                board[x][y]=i;                if(isValidSudoku(x,y,board) && dfs(pos+1,board)) return true;                board[x][y]=‘.‘;            }        }else{            if(dfs(pos+1,board)) return true;        }        return false;    }        void solveSudoku(vector<vector<char> > &board) {        dfs(0,board);    }};