leetcode WiggleSubsequence

public class WiggleSubsequence {
  /**
   * Wiggle Subsequence
   * A sequence of numbers is called a wiggle sequence if 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.
   *
   * Given a sequence of integers, return the length of the longest subsequence that is a wiggle sequence.
   * A subsequence is obtained by deleting some number of elements (eventually, also zero)
   * from the original sequence, leaving the remaining elements in their original order.
   *
   * Example 1:
   *
   * Input: [1,7,4,9,2,5]
   * Output: 6
   * Explanation: The entire sequence is a wiggle sequence.
   * Example 2:
   *
   * Input: [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: [1,2,3,4,5,6,7,8,9]
   * Output: 2
   * Follow up:
   * Can you do it in O(n) time?
   */
  public int wiggleMaxLength(int[] nums) {
    if (nums.length==0 || nums== null){
      return 0;
    }
    else if (nums.length <=2){
      return nums.length;
    }

    Boolean isIncreasing = null;
    int count = 1;
    for (int i=1; i<nums.length; i++){
      if (nums[i] > nums[i-1]){
        if (isIncreasing == null || !isIncreasing){
          count++;
        }
        isIncreasing = true;
      }
      else if (nums[i] < nums[i-1]){
        if (isIncreasing== null || isIncreasing){
          count ++;
        }
        isIncreasing = false;
      }
    }
    return count;
  }

}