Czech ACM Student Chapter
Czech Technical University in Prague
Charles University in Prague
Technical University of Ostrava
Slovak University of Technology
University of Zilina
University of West Bohemia
CTU Open Contest 2017
amusement.c, amusement.cpp, amusement.c11, Amusement.java, amusement.py
It is was late Saturday morning at the end of October. The amusement park was going to be
open that afternoon for the first time after months of prolonged reconstruction.
Josse and Murry were sitting in the basement of the office building at the park gate. They have
just finished debugging their advanced AI system management of all fantastic attractions in the
park. "Work is done," said Josse. "Now for some amusement. Can you think of any algorithmic
"Yes, of course," replied Murry and grinned at his friend from his heavily cluttered desk. "Con-
sider, for example, finite sequences of numbers. For me, the most interesting sequences are those
that end with a long arithmetic sequence. In other words, I like arithmetic sequences that span
from some index to the very last member. As there may be many such subsequences, in order
to truly appreciate how interesting some sequence is, it is necessary to determine which one is
the longest. Here is your initial sequence. You have to find the start of the longest continuous
arithmetic subsequence spanning to its end."
"OK," said Josse when he marked the correct place in the sequence. "That was easy. What
next?" "What next?" Repeated Murry and hesitated for a moment. Then he raised himself
determinedly from the chair. "Let's go out to the park and find some tougher problems there!"
There are more test cases. Each case consists of two lines. The first line contains one integer N
(1 ≤ N ≤ 1 000) specifying the length of the sequence. The second line contains a sequence of
N integers Xi (0 ≤ Xi ≤ 109 ), separated by spaces.
For each test case, print a single line with the index of the first member of the longest continuous
arithmetic subsequence that spans to the end of the given sequence. The index of the first element
in the sequence is always 1.
Output for Sample Input