Sharp thresholds for half-random games II

TL;DR

This paper determines the precise bias thresholds for various classical biased Maker-Breaker games on complete graphs, showing that clever Maker can win quickly even against near-optimal random Breaker strategies.

Contribution

It establishes sharp threshold biases for key graph properties in biased Maker-Breaker games with random Breaker, and demonstrates Maker's rapid winning strategy.

Findings

Threshold bias equals the trivial upper bound for these games.

Clever Maker can win quickly, within logarithmic moves.

Results apply to connectivity, perfect matching, Hamiltonicity, and minimum degree-1 games.

Abstract

We study biased Maker-Breaker positional games between two players, one of whom is playing randomly against an opponent with an optimal strategy. In this work we focus on the case of Breaker playing randomly and Maker being "clever". The reverse scenario is treated in a separate paper. We determine the sharp threshold bias of classical games played on the edge set of the complete graph $K_n$, such as connectivity, perfect matching, Hamiltonicity, and minimum degree-$1$. In all of these games, the threshold is equal to the trivial upper bound implied by the number of edges needed for Maker to occupy a winning set. Moreover, we show that the clever Maker can not only win against an asymptotically optimal bias, but can do so very fast, wasting only logarithmically many moves (while the winning set sizes are linear in $n$).