Connect-4 PopOut

My Master's thesis consisted of computer analyzing a variant of Connect-4 called PopOut. Connect-4 is a classic board game where two players drop pieces in a vertical board and try to make a four-in-row. The variant introduces a new move type that allows players to pop out (remove) their own piece if it is at the bottom of the board. This causes all pieces above to fall down due to gravity.

The new move type has some consequences for computer search. Most importantly, the variant allows players to return to an old position making the game circular. The branching factor (average number of alternative moves) is also increased as is the state space (number of legal positions). Despite these factors, it was widely accepted among expert human players that the first player had an even bigger advantage in the variant than in the original game. My task was to confirm this assumption through computer analysis, which had not been done earlier.

Click here to play against my program in the browser.

Javascript source code

Screenshot of the application implemented in C++ and Qt