题目描述：
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
解法1：贪心思想
class Solution {public int wiggleMaxLength(int[] nums) {if (nums == null || nums.length == 0) return 0;int len = 1;int head = nums[0];Boolean flag = null;for(int num : nums){if(num == head) continue;if(flag == null || flag != num > head){flag = num > head;len++;}head = num;}return len;}
}解法二：动态规划
class Solution {public int wiggleMaxLength(int[] nums) {if(nums == null || nums.length == 0)return 0;int up = 1, down = 1;for(int i = 1; i < nums.length; i++){if(nums[i] > nums[i - 1]){up = down + 1;}else if(nums[i] < nums[i - 1]){down = up + 1;}}return Math.max(up, down);}
}具体分析以后有时间再详细写下来~