I d like to walk in 2 loops over 0 to half of string and the

Question

I d like to walk in 2 loops over 0 to half of string and then end of string back to half this doesn t look like the way to do it ```for i in 0 until halfIndex for j in s length downTo halfIndex println i $ s i j $ s j ```

oday · Answer

halfIndex is `s length 2` let s say 5 for example so the first loop from `0 to 5` and the second from `11 to 5`

Sourabh Rawat · Answer

`for j in s lastIndex downTo halfIndex`

Sourabh Rawat · Answer

Also do you want to nest them or run the loops after one another

oday · Answer

I want to be testing forwards and backwards at the same time with halfIndex being the stopper

oday · Answer

yea not nesting

Sourabh Rawat · Answer

Then you should move the second for loop outside of the first for loop

ephemient · Answer

well you immediately have a OOBE on `s j ` because j = s length initially

ephemient · Answer

if you want to traverse front to back and back to front in lockstep consider ```for i in 0 until halfIndex val j = s lastIndex i println $ s i $ s j ``` or maybe ```val forward = s listIterator val backward = s listIterator s size while forward nextIndex lt backward previousIndex println $ forward next $ backward previous ```

ephemient · Answer

listIterator only works on List as the name implies so that second one is not useful on String

Sourabh Rawat · Answer

< ephemient> I believe your solution won t work for a list string with odd number of items

ephemient · Answer

< Sourabh Rawat> depends on what you want to happen with the middle element what I wrote will skip it just as < oday> s original `0 until halfIndex` would but it s a simple tweak to include it

Sourabh Rawat · Answer

The original code won t skip it The second loop will take it Although it s start condition should be `s lastIndex`

ephemient · Answer

the code as written won t take it because it crashes first the code as described testing forwards and backwards at the same time won t take it either if it s using a `0 until halfIndex` loop

Sourabh Rawat · Answer

the code is not what OP wants That is true and already agreed upon If you were to fix the `s length` thing then the second loop correct ver `s lastIndex downTo halfIndex` will take the middle element

ephemient · Answer

not if it s also using `0 until halfIndex` and stepping both in parallel ` 0 until halfIndex zip lastIndex downTo lastIndex ` will exclude the middle element if odd

oday · Answer

this is what I wanted ```var j = final lastIndex for i in final indices if final i = final j return false else j ``` comparing first and last second and last 1 etc no need for halfIndex turns out wanted to check for palindrome in a certain way

Sourabh Rawat · Answer

typical example of <https xyproblem info > it seems for future references

oday · Answer

except the solution is in the understanding of the problem

ephemient · Answer

in that case you don t need to keep track of `j` that would be equivalent to a tweak to what I wrote with just minor adjustments ```for i in final indices if final i = final final lastIndex i return false ```

ephemient · Answer

if performance isn t a concern that could be more succinctly represented with ```final zip final reversed a b gt if a = b return false ```

oday · Answer

thanks again

Klitos Kyriacou · Answer

Note that your solution does twice the work that would be necessary to check that a string is a palindrome because i and j cross each other and then continue to the end instead of stopping and returning true when they meet half way

oday · Answer

true