Segment Tree From The IMO

Revision en9, by wfe2017, 2017-02-04 14:52:33

Here's the problem (IMO 2013 Problem 1): Assume that k and n are two positive integers. Prove that there exist positive integers m1, ... , mk such that

There is an inductive proof, but some people have issues with induction because they give no insight.

Another solution path is just plugging in formulas and if they're right it generally works out. But there may beno hints as to where the formula came from. My proof and intuition behind my solution has a lot of similarities with how segment trees function.

Think:

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Here's a generalization, which is much easier once you've found the segtree solution to the above problem. Assume that k and n are two positive integers. Prove that there exist positive integers m1, ... , mk such that , where l is an integer and l ≤ 2 × ceil(log2(k / 2 + 1)).

Challenge: Implement the two variants of the problem. In the generalization, you are given k and n, and you are required to output an array that consists of m1, m2, ..., ml.

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  Rev. Lang. By When Δ Comment
en13 English wfe2017 2017-02-08 19:48:16 71
en12 English wfe2017 2017-02-04 20:08:33 144
en11 English wfe2017 2017-02-04 19:35:37 69
en10 English wfe2017 2017-02-04 19:33:57 407
en9 English wfe2017 2017-02-04 14:52:33 604
en8 English wfe2017 2017-02-04 14:17:42 365
en7 English wfe2017 2017-02-04 11:16:24 7 Tiny change: ' $l \leq 2\ceil(log_2' -> ' $l \leq 2 \times ceil(log_2'
en6 English wfe2017 2017-02-04 11:15:55 12 Tiny change: 'd $l \leq log_2(k)+1$. \n\nCha' -> 'd $l \leq 2\ceil(log_2(k/2+1))$. \n\nCha'
en5 English wfe2017 2017-02-04 11:13:54 6 Tiny change: 'er and $l <= log_2(k)+' -> 'er and $l \leq log_2(k)+'
en4 English wfe2017 2017-02-04 11:13:32 211
en3 English wfe2017 2017-02-04 11:11:40 1307 (published)
en2 English wfe2017 2017-02-04 11:03:39 7
en1 English wfe2017 2017-02-04 11:03:15 271 Initial revision (saved to drafts)