Question

I’ve got the assignment to create a very fast nqueens program. So far, Bruteforce algorithm and Backtrack are working, but I’ve found a C program which seems to be faster. Now I’ve tried to convert it from C to Java, however I’m unable to convert the pointers, as I’m not understanding what’s happening with pointers.
These are the lines that have to be converted:

Edit: I’ve updated the conversions to what I’ve understood:

final int[] aStack = new int[MAX_BOARDSIZE * 2];
int bitfield; //That's what I've got so far


//Conversion 1:
register int* pnStack;       -> int pnStack;

//Conversion 2:
pnStack = aStack + 1;        -> pnStack = 1;

//Conversion 3:
pnStack = aStack + 1;        -> pnStack = 1;
*pnStack++ = 0;              -> aStack[pnStack++] = 0;

//Conversion 4:
bitfield = *--pnStack;       -> bitfield = aStack[--pnStack];

//Conversion 5:
*pnStack++ = bitfield;       -> aStack[pnStack++] = bitfield;

//Conversion 7:
pnStack == aStack            -> pnStack == aStack[0] ???????

A solution would be nice, but I’ll try to find it myself if you can explain me what’s going on here. Pointers are the reason I never actually learned c and c++.

Regards,
Dennis Fischer

Answer 1

Inside an array, interpret a pointer just as you would use an index inside the array.

The * means the value in the current position of the index.

So

pnStack = aStack;  <-- int pnStack = 0;
pnStack++;         <-- pnStack++;
bitfield = *pnStack <-- bitfield = aStack[pnStack];
bitfield = *--pnStack <-- bitfield = aStack[--pnStack]; (first decrement index, then retrieve the value)