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;
}
}
```

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