How do I clean up these nested for loops? [closed] - c++

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NOTE: Bad code ahead. You've been warned.
This code iterates through all elements in all 3x3 squares in a Sudoku puzzle. The way shown below is that it gets the coordinate of the upper-left-hand element for each square then iterates through each element in that square. This means that there will be a total of 4 "for" loops needed to just access the correct index, and then another "for" loop to do the correct action.
This code will work (if the retracted code were put in), but it looks very messy and is very hard to read. Is there a better way to do it that eliminates these nested "for" loops?
Thanks in advance.
void Sudoku::updateSquares(int grid[9][9], int possibleSolutions[9][9][10])
{
for (int i = 0; i < 9; i += 3)
{
for (int j = 0; j < 9; j += 3) //for every square:
{
//Other code
//...
//Other code
//updates the possibleSolutions array
for (int k = 0; k < 3; k++)
{
for (int l = 0; l < 3; l++) //for every element in every square:
{
if(grid[i+k][j+l] != 0)
continue;
for (int n = 0; n < 10; n++)
{
if(possibleSolutions[i+k][j+l][n] != 0 && numbers[n] == 0)
{
possibleSolutions[i+k][j+l][n] = 0;
possibleSolutions[i+k][j+l][0] -= 1; //reduce the size, which is held in [][][0]
}
}
}
}
}
}
}

Answer 1

You have implemented something called as "Exhaustive Searching" which is essentially trying out every possible combination of squares.
Have you heard about something called loop unwinding ?
--> Instead of 5 nested For loops use fewer nested loops multiple times; something like 2 nested loops .
Use a dynamic programming approach which is probably O(n^2)
Top Coder DP example.