A range intersection algorithm better than O(n)?

Question

Range intersection is a simple, but non-trivial problem.

Its has been answered twice already:

• Find number range intersection
• Comparing date ra

Answer 1

Overlapping Ranges:

Prep O(n log n):

1. Make a array / vector of the ranges.
2. Sort the vector by the end of the range (break ties by sorting by the start of the range)

3. Make a second vector of ints. This represents the point at which you can stop searching.

   int stop[size];
   stop[size-1] = Ranges[size - 1].start;
   for (int i = size - 2; i >= 0; i--)
   {
       stop[i] = min(Ranges[i].start, stop[i+1]);
   }
   

Search:

1. Use binary search to find the first range with an End value of >= TestRange.Start

2. Iterator starting at the binary search until stop[i] > TestRange.End:

   2a. If the range if the current range is within the TestRange, add it to your result.