1911. Maximum Alternating Subsequence Sum

https://leetcode.com/problems/maximum-alternating-subsequence-sum

Description

The alternating sum of a 0-indexed array is defined as the sum of the elements at even indices minus the sum of the elements at odd indices.

• For example, the alternating sum of [4,2,5,3] is (4 + 5) - (2 + 3) = 4.

Given an array nums, return the maximum alternating sum of any subsequence of nums (after reindexing the elements of the subsequence).

A subsequence of an array is a new array generated from the original array by deleting some elements (possibly none) without changing the remaining elements' relative order. For example, [2,7,4] is a subsequence of [4,2,3,7,2,1,4] (the underlined elements), while [2,4,2] is not.

Example 1:

**Input:** nums = [4,2,5,3]
**Output:** 7
**Explanation:** It is optimal to choose the subsequence [4,2,5] with alternating sum (4 + 5) - 2 = 7.

Example 2:

**Input:** nums = [5,6,7,8]
**Output:** 8
**Explanation:** It is optimal to choose the subsequence [8] with alternating sum 8.

Example 3:

**Input:** nums = [6,2,1,2,4,5]
**Output:** 10
**Explanation:** It is optimal to choose the subsequence [6,1,5] with alternating sum (6 + 5) - 1 = 10.

Constraints:

• 1 <= nums.length <= 105

• 1 <= nums[i] <= 105

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