 Cost-bounded depth-first search

A cost-bounded depth-first search follows the usual depth-first search order but immediately rejects a generated search node whose accumulated path cost exceeds a threshold $L$. It can also return the least rejected path cost, providing the next threshold for iterative lengthening search. Positive step costs ensure that a rejected prefix cannot become a cheaper extension. With finite branching factor and every step costing at least $ϵ>0$, every admitted search node has search depth at most $\lfloor L/ϵ\rfloor$, so the pass terminates. Merely requiring every individual step cost to be positive does not exclude an infinite branch of finite total path cost.