# Wiggle Subsequence

Given an integer array nums, return *the length of the longest wiggle sequence*.

A **wiggle sequence** is a sequence where the differences between successive numbers strictly alternate between positive and negative. The first difference (if one exists) may be either positive or negative. A sequence with fewer than two elements is trivially a wiggle sequence.

For example, [1, 7, 4, 9, 2, 5] is a

**wiggle sequence**because the differences (6, -3, 5, -7, 3) are alternately positive and negative.In contrast, [1, 4, 7, 2, 5] and [1, 7, 4, 5, 5] are not wiggle sequences, the first because its first two differences are positive and the second because its last difference is zero.

A **subsequence** is obtained by deleting some elements (eventually, also zero) from the original sequence, leaving the remaining elements in their original order.

**Example 1:**

**Input****:** nums = [1,7,4,9,2,5]
**Output****:** 6
**Explanation****:** The entire sequence is a wiggle sequence.

**Example 2:**

**Input****:** nums = [1,17,5,10,13,15,10,5,16,8]
**Output****:** 7
**Explanation****:** There are several subsequences that achieve this length. One is [1,17,10,13,10,16,8].

**Example 3:**

**Input****:** nums = [1,2,3,4,5,6,7,8,9]
**Output****:** 2

**Constraints:**

1 <= nums.length <= 1000

0 <= nums[i] <= 1000

**Follow up:** Could you solve this in O(n) time?

**Solution:**

```
public class Solution
{
public int wiggleMaxLength(int[] nums)
{
if (nums.length < 2)
return nums.length;
int prevdiff = nums[1] - nums[0];
int result = prevdiff != 0 ? 2 : 1;
for (int i = 2; i < nums.length; i++) {
int diff = nums[i] - nums[i - 1];
if ((diff > 0 && prevdiff <= 0) || (diff < 0 && prevdiff >= 0)) {
result++;
prevdiff = diff;
}
}
return result;
}
}
```