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Search sorted List<Long> for closest and less than

Lady Bird Johnson234005-Oct-2013

Consider some long called X and a sorted List<Long>. What is the most efficient algorithm to find the index or value in the List<Long> that is (i) less than X, and (ii) The closest to X on the number line (assuming condition (i) has been satsified)?

For example this could be a problem setup:

long X = 500; 
List<Long> foo = new Arraylist<Long>();
foo.add(450L);
foo.add(451L);
foo.add(499L);
foo.add(501L);
foo.add(550L);

Collections.sort(foo); // It's always sorted.

I would like the algorithm to either return 499 or to return the index associated with 499 (in this casei=2).


Updated on 05-Oct-2013

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