Approaches

Constructive and reservoir policies

Build structures that pay off later and survive repeated row rises instead of taking only immediate points.

Structural terminal veto

Keeps the four-move search in charge unless a long simulation favors its second choice. Two independent tests still finished behind the unchanged search.

rejected

Depth-4 search and long outcomes

Judges moves over 25-step continuations, then tries to retain only choices that survive the longer view.

Depth-4 search and long outcomesfeatured

Rollout veto

Keep the depth-4 search's move unless replaying every column forward for twenty-five moves says, across all seven imagined futures, that another one is better.

recorded

Fair expectimax

Look a few moves ahead, take the best column on your own turns, and average over every sampled disc the game might deal.

Fair expectimax

Judging a move by playing the game out

Score each column by simulating the next eight to twenty-four moves with a fast policy on identical imagined futures, instead of by looking a fixed few moves ahead.

rejectedrecorded

Hand-built heuristics and shallow search

Scores visible board traits, adds them together, and plays the highest-valued column.

Hand-built heuristics and shallow search

Rollout

Judge a column by playing twenty-five more moves under several imagined disc streams instead of scoring only the resulting board.

rejected

Lifetime objective

Judge a move by how much longer the game will still last, rather than by how many points it scores right now.

Lifetime objective

Letting a long look-ahead overrule the search

Plays every candidate 25 moves forward and overrides the reference only when one column is clearly better.

rejectedreproduced

Terminal policy iteration

Play every move forward many times, then override the reference only when one move produces clearly longer, higher-scoring games.

Terminal policy iterationfeatured

Public rollout policy iteration

The cheap version uses fifteen shared futures of fifty moves for one improvement step over a simple search.

rejectedrecorded

Terminal policy iteration

Public regenerative B0

Eliminate weak columns cheaply, test the survivors against the reference, and override it only with strong evidence.

rejectedrecorded

Terminal policy iteration

Public survival rollout

Judge each column by survival over thirty-one shared futures of one hundred moves each.

rejected

Terminal policy iteration

The full-strength version uses 255 shared futures of 200 moves and changes the reference move only with 99% confidence in both score and lifetime gains.

rejected

Terminal policy iteration

Terminal rollout

Compare columns by playing each one to the end of the game. This faithful version was unaffordable.