[Haskell-cafe] Data.IntMap union complexity

[Kazu Yamamoto ( 山本和彦 )]

Hello,

> Looking at IntMap's left-biased 'union' function [1], I noticed that the
> complexity is O(n+m) where n is the size of the left map, and m is the size of
> the right map.
> 
> Since insertion [2] is O(min(n, W)) [ where W is the number of bits in an Int
> ], wouldn't it be more efficient to just fold 'insert' over one of the lists
> for a complexity of O(m*min(n, W))? This would degrade into O(m) in the worst
> case, as opposed to the current O(n+m).

Interesting.

I would point out that the original paper "Fast Mergeable Integer
Maps" says that merge is O(n+m). 

I don't know which one is correct.

--Kazu