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Editorial Team
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Asked: 2026-06-08T05:59:06+00:00

Since Java uses a red-black tree to implement the TreeMap class, is the efficiency

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Since Java uses a red-black tree to implement the TreeMap class, is the efficiency of put() and get() lg(N), where N = number of distinct keys, or N = number of insertions/retrievals you plan to do?

For example, say I want to use a 

TreeMap<Integer, ArrayList<String>>

to store the following data:

1 million <1, “bob”> pairs and 1 million <2, “jack”> pairs (the strings get inserted into the arraylist value corresponding to the key)

The final treemap will have 2 keys, with each one storing arraylist of million “bob” or “jack” strings. Is the time efficiency lg(2mil) or lg(2)? I am guessing it’s lg(2) since that’s how a red-black tree works, but just wanted to check.

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1 Answer

  1. Editorial Team

    Performance of a TreeMap with 2 pairs will behave as N=2, regardless of how many duplicate additions were previously made. There is no “memory” of the excess additions so they cannot possibly produce any overhead.

    So yes, you can informally assume that time efficiency is “log 2”.

    Although it’s fairly meaningless as big-O notation is intended to relate to asymptotic efficiency rather than be relevant for small sizes. An O(N^3) algorithm could easily be faster than a O(log N) algorithm for N=2.

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