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.
\r\n\r\n[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.
\r\n
Example 1:
\r\n\r\n\r\nInput: nums = [4,2,5,3]\r\nOutput: 7\r\nExplanation: It is optimal to choose the subsequence [4,2,5] with alternating sum (4 + 5) - 2 = 7.\r\n\r\n\r\n
Example 2:
\r\n\r\n\r\nInput: nums = [5,6,7,8]\r\nOutput: 8\r\nExplanation: It is optimal to choose the subsequence [8] with alternating sum 8.\r\n\r\n\r\n
Example 3:
\r\n\r\n\r\nInput: nums = [6,2,1,2,4,5]\r\nOutput: 10\r\nExplanation: It is optimal to choose the subsequence [6,1,5] with alternating sum (6 + 5) - 1 = 10.\r\n\r\n\r\n
\r\n
Constraints:
\r\n\r\n1 <= nums.length <= 1051 <= nums[i] <= 105一个下标从 0 开始的数组的 交替和 定义为 偶数 下标处元素之 和 减去 奇数 下标处元素之 和 。
\n\n[4,2,5,3] 的交替和为 (4 + 5) - (2 + 3) = 4 。给你一个数组 nums ，请你返回 nums 中任意子序列的 最大交替和 （子序列的下标 重新 从 0 开始编号）。
一个数组的 子序列 是从原数组中删除一些元素后（也可能一个也不删除）剩余元素不改变顺序组成的数组。比方说，[2,7,4] 是 [4,2,3,7,2,1,4] 的一个子序列（加粗元素），但是 [2,4,2] 不是。
\n\n
示例 1：
\n\n输入：nums = [4,2,5,3]\n输出：7\n解释：最优子序列为 [4,2,5] ，交替和为 (4 + 5) - 2 = 7 。\n\n\n
示例 2：
\n\n输入：nums = [5,6,7,8]\n输出：8\n解释：最优子序列为 [8] ，交替和为 8 。\n\n\n
示例 3：
\n\n输入：nums = [6,2,1,2,4,5]\n输出：10\n解释：最优子序列为 [6,1,5] ，交替和为 (6 + 5) - 1 = 10 。\n\n\n
\n\n
提示：
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