376. Wiggle Subsequence

376. 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.

Examples:

Input: [1,7,4,9,2,5]Output: 6The entire sequence is a wiggle sequence.Input: [1,17,5,10,13,15,10,5,16,8]Output: 7There are several subsequences that achieve this length. One is [1,17,10,13,10,16,8].Input: [1,2,3,4,5,6,7,8,9]Output: 2

Follow up: Can you do it in O(n) time?

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

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