madeluccar - 1 year ago 164

Java Question

I know there is a lot of of questions regarding connect 4 check for a win. The issue is that most of other algorithms make my program have runtime errors, because they try to access an index outside of my array.

My algorithm is like this:

`private int checkWin(int[][] gridTable,int rowNum,int colNum, int maxRow, int maxCol)`

{

// For checking whether any win or lose condition is reached. Returns 1 if win or lose is reached. else returns 0

// gridTable[][] is the game matrix(can be any number of rows and columns between 4 and 40)

// colNum is the column number where the last token was placed

// rowNum is the row number where the last token was placed

// maxRow is the number of rows in my grid

// maxCol is the number of columns in my grid

int player = gridTable[rowNum][colNum]; //player ID

int count=0;

// Horizontal check

for (int i=0;i<maxCol;i++)

{

if (gridTable[rowNum][i]==player)

count++;

else

count=0;

if (count>=4)

return 1;

}

//Vertical check

for (int i=0;i<maxRow;i++)

{

if (gridTable[i][colNum]==player)

count++;

else

count=0;

if (count>=4)

return 1;

}

count=0;

// 4 in a row diagonally

for(int i=colNum+1,j=rowNum+1;i<maxRow && j<maxCol;i++,j++)

{

if(gridTable[j][i]!=player)

{

count=1;

break;

}

count++;

}

// 4 in a row diagonally

for(int i=colNum-1,j=rowNum-1;i>=0 && j>=0;i--,j--)

{

if(gridTable[j][i]!=player)

{

count=1;

break;

}

count++;

}

// 4 in a row diagonally

for(int i=colNum+1,j=rowNum-1;i<maxRow && j>=0;i++,j--)

{

if(gridTable[j][i]!=player)

{

count=1;

break;

}

count++;

}

for(int i=colNum-1,j=rowNum+1;i>=0 && j<maxCol;i--,j++)

{ // 4 in a row diagonally

if(gridTable[j][i]!=player)

{

count=1;

break;

}

count++;

}

if(count>=4)

return 1;

return 0;

}

count is the variable that checks for a win if count is equal or more than 4 means they should be 4 or more consecutive tokens of the same player.

THE PROBLEM: sometimes the method checks for a win without being 4 tokens in order and other times does not check for a win when 4 tokens are in order.

Answer Source

Looks like your code is correct for the horizontal and vertical cases. The tricky part is the diagonal case.

Let's try a picture:

For the green lines, your starting row position is 0 ... maxRow - 4. The column would be 0 ... startingRow -

Pseudocode:

```
// top-left to bottom-right - green diagonals
for( rowStart = 0; rowStart < rowMax - 4; rowStart++){
count = 0;
int row, col;
for( row = rowStart, col = 0; row < rowMax && col < colMax; row++, col++ ){
if(gridTable[row][col] == player){
count++;
if(count >= 4) return 1;
}
else {
count = 0;
}
}
}
// top-left to bottom-right - red diagonals
for( colStart = 1; colStart < colMax - 4; rowStart++){
count = 0;
int row, col;
for( row = 0, col = colStart; row < rowMax && col < colMax; row++, col++ ){
if(gridTable[row][col] == player){
count++;
if(count >= 4) return 1;
}
else {
count = 0;
}
}
}
```

You could do something similar for diagonals going the other way (from bottom-left to top-right).