ALTSEQ – Alternating Sequences Solution

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SPOJ Solution

ALTSEQ Statement

Given an array a of N integers a1, a2, a3, … aN you have to find the longest alternating sub-sequence of this array .
An alternating sequence b1, b2 … bk, k>=1 is a sequence that has the 2 following properties:
1.|b1|<|b2|<|b3|<…..<|bk|
2. The signs alternate between adjacent elements, i.e, if b1 > 0 then b2<0, b3 >0 and so on. Alternatively, if b1<0, then b2>0, b3<0 and so on.
A sub sequence of array a is a sequence obtained by dropping some elements of the array a. Here is the formal definition.
It is guaranteed that the array a contains no element equal to 0.

Constraints

1<=N<=5000 |ai|<=10^9, ai not equal to 0.

Input

The first line contains a single integer N, denoting the size of the array. The next line contains N integers , denoting the array a.

Output

Print a single integer – the length of the longest alternating sub-sequence.

ALTSEQ Solution

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