Leetcode 376. Wiggle Subsequence (Medium) (cpp)

Leetcode 376. Wiggle Subsequence (Medium) (cpp)

Tag: Dynamic Programming, Greedy

Difficulty: Medium

/*

376. Wiggle Subsequence (Medium)

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
Follow up:
Can you do it in O(n) time?
*/
class Solution {
public:
int wiggleMaxLength(vector<int>& nums) {
int _size = nums.size(), p = 1, n = 1;
for (int i = 1; i < _size; i++){
if (nums[i] > nums[i-1]) p = n + 1;
else if(nums[i] < nums[i-1]) n = p + 1;
}
return _size == 0 ? 0 : max(p, n);
}
};