Why it matters

Bidirectional speeds up long paths. Understanding shapes search design.

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The architecture

Forward BFS from source.

Backward BFS from target.

Stop when frontiers meet.

Bidirectional searchForward BFSfrom sourceBackward BFSfrom targetMeetat frontierb^(d/2) vs b^d exponential improvement; needs backward transitions
Bidirectional.
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How it works end to end

Requires backward transitions.

Meet condition careful.

Bidirectional Dijkstra + A* variants.