Question

I have a set of ranges :

Range1 —- (0-10)

Range2 —- (15-25)

Range3 —- (100-1000) and likewise.
I would like to have only the bounds stored since storing large ranges , it would be efficient.

Now I need to search for a number , say 14 . In this case, 14 is not present in any of the ranges whereas (say a number) 16 is present in one of the ranges.

I would need a function

bool search(ranges, searchvalue)
{
    if searchvalues present in any of the ranges
        return true;
    else
        return false;
}

How best can this be done ? This is strictly non-overlapping and the important criteria is that the search has to be most efficient.

Answer 1

One possibility is to represent ranges as a pair of values and define a suitable comparison function. The following should consider one range less than another if its bounds are smaller and there is no overlap. As a side effect, this comparison function doesn’t let you store overlapping ranges in the set.

To look up an integer n, it can be treated as a range [n, n]

#include <set>
#include <iostream>

typedef std::pair<int, int> Range;
struct RangeCompare
{
    //overlapping ranges are considered equivalent
    bool operator()(const Range& lhv, const Range& rhv) const
    {   
        return lhv.second < rhv.first;
    } 
};

bool in_range(const std::set<Range, RangeCompare>& ranges, int value)
{
    return ranges.find(Range(value, value)) != ranges.end();
}

int main()
{
    std::set<Range, RangeCompare> ranges;
    ranges.insert(Range(0, 10));
    ranges.insert(Range(15, 25));
    ranges.insert(Range(100, 1000));
    std::cout << in_range(ranges, 14) << ' ' << in_range(ranges, 16) << '\n';
}