finding triangulars from array

Question

zero-indexed array A consisting of N integers is given. A triplet (P, Q, R) is triangular if and

A[P] + A[Q] > A[R], 
A[Q] + A[R] > A[P], 
A[R] + A[P         


        

Answer 1

There are many in-place sorts; use one of them to sort the array - say comb sort for smaller ones (time complexity O(N^2)) or heap sort (complexity O(N log(N)).

Once you have sorted array, problem should be whether there is a set of 3 numbers where A[X] > (A[X-1] + A[X+1]) / 2 i.e. middle number is greater than average of preceding & succeeding numbers (sadly this is a guess, I don't have a real basis - if its incorrect I hope someone corrects me, but there should be some good way to redefine the 'triangle' requirement to be more easily checked).

Now you just have an O(1) iteration over the sorted array to check whether the condition is true, hence overall complexity will be that of the sorting algorithm (best case N logN)