longestAlternatingSubsequence function

int longestAlternatingSubsequence(List<int> nums)

🔄 Alternating Subsequences (Longest Alternating Subsequence)

Returns the length of the longest alternating (up/down) subsequence in nums.

Time Complexity: O(n) Space Complexity: O(1)

Implementation

int longestAlternatingSubsequence(List<int> nums) {
  if (nums.isEmpty) 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 up > down ? up : down;
}