[Leetcode] Sudoku Solver

Sudoku Solver

Write a program to solve a Sudoku puzzle by filling the empty cells.

Empty cells is indicated by the character ‘.‘ .

Assume that there would be is only one unique solution.

Ideas:

DFS searches for all possible solutions, each with a space starting at 1-9, and the IsValid () function determines whether the space can be placed in this number. If it can, continue with Dfs recursion, if it cannot proceed to the next number. If there is still no feasible solution after traversing 1-9, the preceding space is not filled with the wrong number, only the previous number can be changed back. This traversal, until the last space still satisfies the condition, indicates that a workable solution has been found. A variable flag flag is used to determine if a viable solution is found. If no feasible solution is found, the current number is restored to the initial state (.), and the loop is resumed, and if it is found, it is returned directly and no longer loops, leaving recursively. This flag is important, if the flag is not available, although the possible solution is found, but the rest of the loop will continue to exit recursively, the value of board[i][j] will change, so the results are very strange when the recursion is rolled out.

In fact, there is a method at night, the idea is similar, just to change the DFS () function to return the value, but no longer void. This returns true if a workable solution is found, otherwise false is returned.

Exercises

classSolution { Public:    BOOLFlag =false;//determine if a workable solution is found    BOOLIsValid (vector<vector<Char> > &board,intRowintCol) {         for(intj=0;j<9; j + +)            if(J!=col && Board[row][col] = =Board[row][j])return false;  for(intI=0;i<9; i++)            if(I!=row && Board[row][col] = =Board[i][col])return false; intx = row/3*3; inty = col/3*3;  for(intI=0;i<3; i++)             for(intj=0;j<3; j + +)                if(X+i!=row && y+j!=col && board[row][col] = = board[x+i][y+J])return false; return true; }    voidDFS (vector<vector<Char> > &Board) {        intK;  for(intI=0;i<9; i++)             for(intj=0;j<9; j + +) {                if(board[i][j]=='.') {                     for(k=0;k<9; k++) {Board[i][j]= k +'1'; if(IsValid (board,i,j)) DFS (board); if(!flag)//If no workable solution is found, the restorationBOARD[I][J] ='.'; Else           //have found a workable solution, return directly, not continue the next cycle                            return; }                    if(k==9)//Maintenance If the fill 1-9 is not satisfied, the previous results have a problem                        return; }                if(i==8&& j==8)//found a workable solution.Flag =true; }    }        voidSolvesudoku (vector<vector<Char> > &Board)    {DFS (board); }};

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Something:

As in the idea, you can turn the DFS () function into a function that returns a bool type, and feel that this method should be a little more awesome. Just put out two of these methods.

Http://www.cnblogs.com/ganganloveu/p/3828401.html and Http://www.cnblogs.com/panda_lin/archive/2013/11/04/sudoku_solver.html

[Leetcode] Sudoku Solver