I already asked for help here, but nobody answer, and it really frustrating, I am trying to write a code that solve a Sudoku in recursive function (backtracking), here is the code:
#include <stdio.h>
#include <windows.h>
#define SIZE 9
#define SQUARE_SIZE 3
void print(int arrBoard[SIZE][SIZE])
{
system("cls");
int i, j;
for (i = 0; i < SIZE; i++)
{
if (i % 3 == 0) printf("_ _ _ _ _ _ _ _ _ _ _ _\n");
for (j = 0; j < SIZE; j++)
{
if (j % 3 == 0) printf("| ");
printf("%d ", arrBoard[i][j]);
}
printf("\n");
}
Sleep(100);
}
BOOL IsValidRow(int arrBoard[SIZE][SIZE], int iNum, int iRow)
{
int iCol;
for (iCol = 0; iCol < SIZE; iCol++)
if (arrBoard[iRow][iCol] == iNum) return FALSE;
return TRUE;
}
BOOL IsValidCol(int arrBoard[SIZE][SIZE], int iNum, int iCol)
{
int iRow;
for (iRow = 0; iRow < SIZE; iRow++)
if (arrBoard[iRow][iCol] == iNum) return FALSE;
return TRUE;
}
BOOL IsValidSquare(int arrBoard[SIZE][SIZE], int iNum, int iRow, int iCol)
{
iRow-= (iRow % SQUARE_SIZE);
iCol-= (iCol % SQUARE_SIZE);
int i, j;
for(i = 0; i < SQUARE_SIZE; i++)
for (j = 0; j < SQUARE_SIZE; j++)
if (arrBoard[iRow + i][iCol + j] == iNum) return FALSE;
return TRUE;
}
BOOL IsValid(int arrBoard[SIZE][SIZE], int iNum, int iRow, int iCol)
{
if (IsValidRow(arrBoard, iNum, iRow) == FALSE) return FALSE;
if (IsValidCol(arrBoard, iNum, iCol) == FALSE) return FALSE;
if (IsValidSquare(arrBoard, iNum, iCol, iRow) == FALSE) return FALSE;
return TRUE;
}
BOOL _Solve(int arrBoard[SIZE][SIZE], int iRow, int iCol)
{
if (iRow == 9) return TRUE;
if (arrBoard[iRow][iCol])
{
iRow = (iCol == 8) ? iRow + 1 : iRow;
iCol = (iCol == 8) ? 0 : iCol + 1;
if(_Solve(arrBoard, iRow, iCol)) return TRUE;
return FALSE;
}
int iNewNum, iOldRow, iOldCol;
for (iNewNum = 1; iNewNum <= SIZE; iNewNum++)
{
if (IsValid(arrBoard, iNewNum, iRow, iCol))
{
arrBoard[iRow][iCol] = iNewNum;
print(arrBoard);
iOldRow = iRow; iOldCol = iCol;
iRow = (iCol == 8) ? iRow + 1 : iRow;
iCol = (iCol == 8) ? 0 : iCol + 1;
if (_Solve(arrBoard, iRow, iCol)) return TRUE;
iRow = iOldRow; iCol = iOldCol;
arrBoard[iRow][iCol] = 0;
}
}
return FALSE;
}
int main(void)
{
int arrBoard[SIZE][SIZE] =
{0, 1, 0, 3, 6, 4, 0, 2, 0,
6, 0, 0, 0, 0, 0, 0, 9, 7,
0, 0, 0, 9, 0, 7, 0, 0, 0,
0, 0, 6, 1, 0, 2, 8, 0, 0,
1, 9, 8, 0, 0, 0, 0, 3, 2,
0, 0, 7, 8, 0, 3, 9, 0, 0,
0, 0, 0, 7, 0, 8, 0, 0, 0,
4, 0, 0, 0, 0, 0, 0, 0, 3,
0, 2, 0, 4, 5, 6, 0, 1, 0};
_Solve(arrBoard, 0, 0);
fflush(stdin);
getchar();
return 0;
}
its not the real code (just because the UI isnt important now). so what I did here is to print the board every time it change any cell. I saw one mistake while it tried to solve, when it reached to cell at row: 2 col: 6 (in index its [1][5]), it skip on the number 1 (which is the real answer), because it didnt try one, it cannot solve the rest of the sudoku. i cant find out why it doesnt work.
You've already accomplished the first step, identifying where and when the problem occurs. With the help of a debugger, you can step through _Solve
when iRow
is 1 and iCol
is 5. Here's what I see, just looking at the first point when your problem occurs:
IsValid(arrBoard, iNewNum, iRow, iCol)
returns FALSE
.
Stepping into that method, IsValidSquare(arrBoard, iNum, iCol, iRow)
is returning FALSE
.
Looking again at that line, it seems a bit odd that you've got iCol
before iRow
, when your pattern elsewhere is row-then-column. Comparing the call to the declaration/definition, it looks like you've mixed up the parameters at the call-site.
Fixing the order of the parameters for that call to IsValidSquare
and re-running results in a solution.
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