What is the time complexity of this loop?


Is it $O(n)$ as we are increasing $j$ linearly?

  • $\begingroup$ Hint: j is actually the Gaussian sum. $\endgroup$
    – kelalaka
    Nov 17, 2019 at 10:09
  • $\begingroup$ Cant understand, if you can provide an explanation it will be of much help, even I have no answer manual to confirm, nor its an assignment, if I left this without understanding, it will remain like this for me $\endgroup$
    – Turing101
    Nov 17, 2019 at 10:27

1 Answer 1


Here are the values of $j$ at the end of each iteration: $$ 1,3,6,10,15,21,28,36,45,55,\ldots $$ More generally, after $t$ iterations, $j = 1 + \cdots + t = \binom{t+1}{2} = \Theta(t^2)$. Therefore the loop halts after $\Theta(\sqrt{n})$ iterations.

  • $\begingroup$ Thanks a ton .. :) $\endgroup$
    – Turing101
    Nov 17, 2019 at 11:43

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