ABC Problem

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You are given a collection of ABC blocks (e.g., childhood alphabet blocks). There are 20 blocks with two letters on each block. A complete alphabet is guaranteed amongst all sides of the blocks. The sample collection of blocks:

(B O) (X K) (D Q) (C P) (N A) (G T) (R E) (T G) (Q D) (F S) (J W) (H U) (V I) (A N) (O B) (E R) (F S) (L Y) (P C) (Z M)