i'm reading a c++ implementation of a connect 4 ai (minmax with alpha-beta pruning) by @balkarjun and ...
i love that they represented the board with just two u64 integers - one for each player. a bit is set to 1 where a player's piece has been dropped ...
(code available here: https://github.com/balkarjun/ConnectFourAI/)
and the win checking logic is just pure poetry. it checks one player at a time and does bit shifts that result in a non-zero value if and only if there are 4 pieces (four ones) in any of the winning directions.
![code that checks one player at a time and does bit shifts that would result in a non-zero value only if there are 4 pieces (four ones) in one of the winning directions.
int check_win() {
for (int idx = 0; idx <= 1; idx++) {
u64 board = bitboards[idx];
if ((board & (board >> 7) & (board >> 14) & (board >> 21)) != 0) return idx; // horizontal
if ((board & (board >> 1) & (board >> 2) & (board >> 3)) != 0) return idx; // vertical
if ((board & (board >> 8) & (board >> 16) & (board >> 24)) != 0) return idx; // positive diagonal
if ((board & (board >> 6) & (board >> 12) & (board >> 18)) != 0) return idx; // negative diagonal
}
return -1;
}](https://media.tech.lgbt/media_attachments/files/113/330/068/427/587/362/original/7b6223d32a1006ef.png "code that checks one player at a time and does bit shifts that would result in a non-zero value only if there are 4 pieces (four ones) in one of the winning directions.
int check_win() {
for (int idx = 0; idx <= 1; idx++) {
u64 board = bitboards[idx];
if ((board & (board >> 7) & (board >> 14) & (board >> 21)) != 0) return idx; // horizontal
if ((board & (board >> 1) & (board >> 2) & (board >> 3)) != 0) return idx; // vertical
if ((board & (board >> 8) & (board >> 16) & (board >> 24)) != 0) return idx; // positive diagonal
if ((board & (board >> 6) & (board >> 12) & (board >> 18)) != 0) return idx; // negative diagonal
}
return -1;
}")