【专题】 考虑每一项对结果到的贡献

常见的是给你一个数组，然后给你一个指标， 让你求这个指标的总和。

比如给你一个数组， 给你一个子数组最大值的指标， 让你求所有子数组最大值的总和。

我们可以考虑数组每一项装结果的贡献， 然后将其累加即可。

题目：

- https://leetcode.cn/problems/sum-of-subsequence-widths/
- https://leetcode.cn/problems/sum-of-subarray-ranges/

Start by reading the issue description and the two linked LeetCode problems: Sum of Subsequence Widths and Sum of Subarray Ranges. Determine where this topic belongs in the repository and document the contribution-based approach, with explanations or solutions for both referenced problems; done means the topic is complete and understandable to readers.

Written by the indexing model from the issue text.