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    <p>I can think of a number of possible solutions for the more general problem where the ranges are not uniform and there are 'holes'. The simplest are:</p> <ol> <li>Simply populate a Map for all valid key values, with multiple keys mapping to the same value. Assuming that you use HashMaps, this should be the most time efficient (O(1) lookups), though you have more work at setup time and you use more space.</li> <li>Use a NavigableMap and use <code>floorEntry(key)</code> to do the lookups. This should be less time efficient (O(log(N) lookups) but more space efficient.</li> </ol> <p>Here's a solution using NavigableMaps that allows for 'holes' in the mapping.</p> <pre><code>private static class Range { public int upper, value; ... } NavigableMap&lt;Integer, Range&gt; map = new TreeMap&lt;Integer, Range&gt;(); map.put(0, new Range(3, 0)); // 0..3 =&gt; 0 map.put(5, new Range(10, 1)); // 5..10 =&gt; 1 map.put(100, new Range(200, 2)); // 100..200 =&gt; 2 // To do a lookup for some value in 'key' Map.Entry&lt;Integer,Range&gt; entry = map.floorEntry(key); if (entry == null) { // too small } else if (key &lt;= entry.getValue().upper) { return entry.getValue().value; } else { // too large or in a hole } </code></pre> <p>On the other hand, if there are no 'holes' the solution is simpler:</p> <pre><code>NavigableMap&lt;Integer, Integer&gt; map = new TreeMap&lt;Integer, Integer&gt;(); map.put(0, 0); // 0..4 =&gt; 0 map.put(5, 1); // 5..10 =&gt; 1 map.put(11, 2); // 11..200 =&gt; 2 // To do a lookup for some value in 'key' if (key &lt; 0 || key &gt; 200) { // out of range } else { return map.floorEntry(key).getValue(); } </code></pre>
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    1. COThis is very good use of the existing TreeMap to do a simple range search. Note that if there are overlapping intervals, then the approach will return that interval with the closest lower key to the lookup key. Similarly, this approach does not support a search for all overlapping intervals containing a given search key, as discussed in http://stackoverflow.com/questions/1580185/data-structure-for-quick-time-interval-look-up
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    2. COIf there are overlapping ranges, then the ranges are (most likely) incorrectly specified. At least, that is my reading of THIS question.
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