We provide an algorithm for computing a planar morph between any two planar straight-line drawings of any n-vertex plane graph in O(n) morphing steps, thus improving upon the previously best known O(n~2) upper bound. Furthermore, we prove that our algorithm is optimal, that is, we show that there exist two planar straight-line drawings Γ_s and Γ_t of an n-vertex plane graph G such that any planar morph between Γ_s and Γ_t requires Ω(n) morphing steps.
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