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Given a set of strings (building blocks), find the length of the smallest string such that there is more than one way to build it.
For example, if the set of building block strings is {"10", "01", "101"}, the smallest string that can be formed in multiple ways is "10101", since it can be constructed by concatenating "10" + "101" or "101" + "01". Therefore, the answer is 5. However, in the case of the set {"AB", "BA", "ABB"}, there is no string that can be constructed in multiple ways from the building blocks. Therefore, the answer in this case is -1.
How can we solve this problem?
