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: 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
AC代码，runtime 0ms.
class Solution {
public:
int wiggleMaxLength(vector<int>& nums) {
if(nums.empty())return ;
int ret=,length=nums.size(),diff,bg=;
for(;bg<length;bg++){
diff=nums[bg]-nums[bg-];
if(diff!=){
ret++;
break;
}
if(bg==length)return ret;
}
for(int i=bg+;i<length;i++){
int tmpdiff=nums[i]-nums[i-];
if(tmpdiff==)continue;
if(tmpdiff*diff<){
diff=tmpdiff;
ret++;
}
}
return ret;
}
};