Would you help me to write an algorithm using array structure for the question above?
(There exists some challenges that require to use the best startegy, but here we don't. Even if you are able to win, you are allowed to make a tie)
Play tic-tac-toe as the second player, and you're not allowed to lose.
I/O method may be:
Input may be the current chessboard(always your last re...
Given an array a that contains only numbers in the range from 1 to a.length, find the first duplicate number for which the second occurrence has the minimal index. In other words, if there are more than 1 duplicated numbers, return the number for which the second occurrence has a smaller index th...
Left and right Riemann sums are approximations to definite integrals. Of course, in mathematics we need to be very accurate, so we aim to calculate them with a number of subdivisions that approaches infinity, but that's not needed for the purposes of this challenge. You should instead try to writ...
Given an array a that contains only numbers in the range from 1 to a.length, find the first duplicate number for which the second occurrence has the minimal index. In other words, if there are more than 1 duplicated numbers, return the number for which the second occurrence has a smaller index th...
Python 3, 94 92 bytes
O(n) time and O(1) extra memory.
def f(a):
r=-1
for i in range(len(a)):t=abs(a[i])-1;r=[r,i+1][a[t]<0>r];a[t]*=-1
return r
Try it online!
Source of the algorithm.
Explanation
The basic idea of the algorithm is to run through each element from left to right, keep ...
Rhombus sequence
Tags: code-golf math sequence
Imagine enumerating the elements of rhombi that which grow [1],[1,3,1],[1,3,5,3,1],… (only odd numbers such that they align nicely). This would look like as follows, note that you always begin enumerating with 1:
01
1 ...
A doubly linked list is a data structure in which each node has a value as well as "links" to both the previous and next nodes in the list. For example, consider the following nodes with values 12, 99, and 37:
Here, the nodes with values 12 and 99 point to their respective next nodes, with val...
What is the shortest way we can express the function
f(a,b)(c,d)=(a+c,b+d)
in point-free notation?
pointfree.io gives us
uncurry (flip flip snd . (ap .) . flip flip fst . ((.) .) . (. (+)) . flip . (((.) . (,)) .) . (+))
which with a little bit of work can be shortened to
uncurry$(`flip`...
The idea of this is mainly from BIO 2017 q1. I got the idea for posting this challenge from my Binary Sequences challenge, since lots of people seemed to like it.
Also, this is the first challenge I've posted without posting on the sandbox. I'll delete it if no one likes it.
Rules
Take in a se...
I know there's a desire on PPCG for challenges to be flexible in terms of what they allow for input and output. However, I think there is an argument to be made that ascii-art is a special case, and should be stricter about the permitted output formats.
As a case in point, there was a recent asc...
Today while playing with my kids I noticed that an apparently simple toy in the park hid a challenge.
The wheel has a triangle that points to a number, but also has three circles that point to the numbers every 90 degrees from the first one. So:
Challenge (really simple)
Given an integer be...
Once, as a child, I found a spider in my parents' garden. I remember catching it in a jar because I thought it looked unusual, but I never figured out what kind of spider it was and unfortunately didn't get any pictures. I've been looking for it in books and on the Internet since, based on memory...
