select two non overlapping segment such that sum of their length minimum. O(n) eg. [2,5], [4,6], [6,7]

ans-6 explanation 2 is overlapped with first and third but 1 and 3 is not ans-(5-2+1)+(7-6+1)=6 1<=n<=10^6 timeLimit-1 second

has any GM or LGM develop some standard algorithm like-dijkstra or data structure like-fenwick tree or something?

How people generate large test case for hacking phase after contest?