Pending Doubt from last 5 days

#1

Raise a doubt for Sudoku Solver problem 5 days ago and also tried to follow up with some TA’s but hard luck.

Please look into this and close this at priority.

#2

@PThak2018 Doubt on recursion logic is this the doubt?

#3

hi @PThak2018 even the last code you gave is giving some syntax error, please correct that first.

#4

yes, this is the one.

#5

You are not referring updated code. Check below code for your reference and please go through the entire comment section where I raised my doubt specifically.

#6

@PThak2018 you dont have to have a pair for each configuration and whether its solvable or not, you can simply have the return type of the “solve” function as bool, and you can check from there if a particular configuration is solvable or not. We pass the sudoku by reference so any changes made anywhere in the program are reflected in the sudoku.
I am attaching a function here and explaining it below as well, please see

base case: if n reaches i, it means there are no more rows to be traversed and the sudoku is solved. at this point, print the sudoku. if j >= 9, then we can simply make a recursive call for the next row and start from the 0th column. If a column if already filled, you dont have to do anything, so simply call for next column. To solve, we try putting 1-9 numbers in it, and call for rest of the sudoku.

bool sudokuSolver(int sudoku[9][9], int n, int i = 0, int j = 0){
	//base case
	if(i == n){
		//print sudoku
		for(int x = 0; x < n; x++){
			for(int y = 0; y < n; y++){
				cout << sudoku[x][y] << " ";
			}
			cout << endl;
		}
		return true;
	}
	//row change
	if(j == n){
		return sudokuSolver(sudoku, n, i + 1, 0);
	}
	//non-empty
	if(sudoku[i][j] != 0){
		return sudokuSolver(sudoku, n, i, j + 1);
	}
	//solve
	for(int number = 1; number <= n; number++){
		if(isValid(sudoku, n, i, j, number)){
			sudoku[i][j] = number;
			bool isSolvable = sudokuSolver(sudoku, n, i, j + 1);
			if(isSolvable){
				return true;
			}
		}
	}
	sudoku[i][j] = 0;
	return false;
}
#7

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