Problem A
Zigzag
A sequence of integers is said to Zigzag if adjacent elements alternate between strictly increasing and strictly decreasing. Note that the sequence may start by either increasing or decreasing. Given a sequence of integers, determine the length of the longest subsequence that Zigzags. For example, consider this sequence:
1 2 3 4 2
There are several Zigzagging subsequences of length $3$:
1 3 2 1 4 2 2 3 2 2 4 2 3 4 2
But there are none of length greater than $3$, so the answer is $3$.
Input
Each input will consist of a single test case. Note that your program may be run multiple times on different inputs. The first line of input contains an integer $n$ ($1 \le n \le 1\, 000\, 000$) which is the number of integers in the list. Each of the following $n$ lines will have an integer $k$ ($1 \le k \le 1\, 000\, 000$).
Output
Output a single integer, which is the length of the longest Zigzagging subsequence of the input list.
Sample Input 1 | Sample Output 1 |
---|---|
5 1 2 3 4 2 |
3 |
Sample Input 2 | Sample Output 2 |
---|---|
6 1 1 1 1 1 1 |
1 |