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Rev

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Find the largest number n positions away from n

_{A sequel to this question.}

Task

Given an array of positive integers, find the largest element k for which:

There exists some positive integer distance n, so that the element in the array located n places to the left or right from k equals n.

The array is guaranteed to contain at least one element satisfying this condition.

The shortest code (in bytes) wins. You may choose whichever I/O format you like.

Example

Given the input

[4, 6, 7, 9, 3, 6, 5, 7, 2]

The eligible values are:

The 4, as there is a 7 located 7 positions to its right
The first 6, as there is a 3 located 3 positions to its right
The 3, as there is a 4 located 4 positions to its left
The 5, as there is a 2 located 2 positions to its right
The second 7, as there is a 3 located 3 positions to its left.

Of these values, the largest is 7.

Test cases

[1, 13] → 13
[2, 9, 8, 3, 72, 2] → 8
[5, 28, 14, 5, 6, 3, 4, 7] → 14
[1, 3, 5, 15, 4, 1, 2, 6, 7, 7] → 7
[5, 1, 3, 5, 2, 5, 5, 8, 5, 1, 5, 1, 2, 3] → 5
[5, 12, 2, 5, 4, 7, 3, 3, 6, 2, 10, 5, 5, 5, 4, 1, 8, 5] → 10

Answer*

# Pyth, <s>19</s> 17 bytes

*Thanks to @Pietu1998 for -2 bytes*

eS@LQ@UQs.e,-kb+b

A program that takes input of a list on STDIN and prints the result.

[Try it online](https://pyth.herokuapp.com/?code=eS%40LQ%40UQs.e%2C-kb%2Bb&test_suite=1&test_suite_input=%5B1%2C+13%5D%0A%5B2%2C+9%2C+8%2C+3%2C+72%2C+2%5D%0A%5B5%2C+28%2C+14%2C+5%2C+6%2C+3%2C+4%2C+7%5D%0A%5B1%2C+3%2C+5%2C+15%2C+4%2C+1%2C+2%2C+6%2C+7%2C+7%5D%0A%5B5%2C+1%2C+3%2C+5%2C+2%2C+5%2C+5%2C+8%2C+5%2C+1%2C+5%2C+1%2C+2%2C+3%5D%0A%5B5%2C+12%2C+2%2C+5%2C+4%2C+7%2C+3%2C+3%2C+6%2C+2%2C+10%2C+5%2C+5%2C+5%2C+4%2C+1%2C+8%2C+5%5D&debug=0)

**How it works**

eS@LQ@UQs.e,-kb+b Program. Input: Q
 .e Map over Q (implicit input fill) with elements as b and indices as k:
 -kb k-b
 +b k+b (Implicit fill with k)
 , 2-element list of those (possible indices)
 s Flatten that
 UQ Yield [0, 1, 2, 3..., len(Q)-1]
 @ Filter the flattened list by presence in the above, removing invalid
 indices
 @LQ Index into Q at those indices
 S Sort that
 e Yield the last element of that, giving the maximum
 Implicitly print

If this is an answer to a challenge…

…Be sure to follow the challenge specification. However, please refrain from exploiting obvious loopholes. Answers abusing any of the standard loopholes are considered invalid. If you think a specification is unclear or underspecified, comment on the question instead.
…Try to optimize your score. For instance, answers to code-golf challenges should attempt to be as short as possible. You can always include a readable version of the code in addition to the competitive one. Explanations of your answer make it more interesting to read and are very much encouraged.
…Include a short header which indicates the language(s) of your code and its score, as defined by the challenge.

More generally…

…Please make sure to answer the question and provide sufficient detail.
…Avoid asking for help, clarification or responding to other answers (use comments instead).

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\$\begingroup\$ }# is the same as @. Also, if you rearrange the last bit to ,-kb+bk you can remove the last k since Pyth auto-inserts it. \$\endgroup\$

PurkkaKoodari
– PurkkaKoodari

2016年09月22日 05:12:46 +00:00
Commented Sep 22, 2016 at 5:12
\$\begingroup\$ @Pietu1998 Thanks. I didn't know about the implicit fill for enumerate; does that work for any other map-type functions? \$\endgroup\$

TheBikingViking
– TheBikingViking

2016年09月22日 15:51:48 +00:00
Commented Sep 22, 2016 at 15:51
\$\begingroup\$ Works for any lambda, it autofills the rest of any lambda with the first lambda variable. \$\endgroup\$

PurkkaKoodari
– PurkkaKoodari

2016年09月22日 16:15:41 +00:00
Commented Sep 22, 2016 at 16:15

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