Data structures that can map a range of keys to a value

Question

I am trying to find a data structure that takes in a particular value from a range of values and map it to a key.

For example, I have the following conditions:

Answer 1

A HashMap will not work for mapping ranges to values unless you find a way to generate a hashcode for ranges and single values in there that matches. But below approach could be what you are looking for

public class RangeMap {
    static class RangeEntry {
        private final double lower;
        private final double upper;
        private final Object value;
        public RangeEntry(double lower, double upper, Object mappedValue) {
            this.lower = lower;
            this.upper = upper;
            this.value = mappedValue;
        }
        public boolean matches(double value) {
            return value >= lower && value <= upper;
        }
        public Object getValue() { return value; }
    }

    private final List entries = new ArrayList();
    public void put(double lower, double upper, Object mappedValue) {
        entries.add(new RangeEntry(lower, upper, mappedValue));
    }
    public Object getValueFor(double key) {
        for (RangeEntry entry : entries) {
            if (entry.matches(key))
                return entry.getValue();
        }
        return null;
    }
}

You could do

RangeMap map = new RangeMap();
map.put(1, 2.9, "A");
map.put(4, 6, "B");

map.getValueFor(1.5); // = "A"
map.getValueFor(3.5); // = null

It's not very efficient since it's just iterating over a list and it will in that state not complain if you put conflicting ranges in there. Will just return the first it finds.

P.S.: mapping like this would be mapping a range of keys to a value