Backtracking all answers

Question

I have this code here. It works fine when you're solving for a solution to a sudoku problem.

int solveBoard(int board[SIZE][SIZE], int rowPos, int colPos) {
    int newValueToCheck, oldRowPos, oldColPos;
    if (rowPos == SIZE) return 1;
    if (board[rowPos][colPos] != 0) {
        if (colPos == SIZE - 1) {
            rowPos++;
            colPos = 0;
        } else colPos++;
        if (solveBoard(board, rowPos, colPos) == 1) return 1;
        return 0;
    } for (newValueToCheck = 1; newValueToCheck <= SIZE; newValueToCheck++)
        if (checkBoard(board, newValueToCheck, rowPos, colPos) == 1) {
            board[rowPos][colPos] = newValueToCheck;
            oldRowPos = rowPos; 
            oldColPos = colPos;
            if (colPos == SIZE - 1) {
                rowPos++;
                colPos = 0;
            } else colPos++;
            if (solveBoard(board, rowPos, colPos) == 1) return 1;
            rowPos = oldRowPos;
            colPos = oldColPos;
            board[rowPos][colPos] = 0;
        }
    return 0;
}

Only thing is, I'd like to get all possible answers. How will I modify this and get all the possible answers.

Answer 1

Don't backtrack the search when a solution has been found. So, make a simple recursive call at the place you try new values and ignore its return value:

solveBoard(board, rowPos, colPos);

and then you every solution at the tail of the recursion:

if (rowPos == SIZE) printSolution(); return 1;