最长摆动子序列
376. Wiggle Subsequence (Medium)
题目描述：
给定一个数组，求出其最长摆动子序列
Input: [1,7,4,9,2,5]
Output: 6
The entire sequence is a wiggle sequence.
Input: [1,17,5,10,13,15,10,5,16,8]
Output: 7
There 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
代码：
public int wiggleMaxLength(int []nums){
if(nums==null||nums.length==0)
return 0;
int up=1;
int 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);
}