大佬加个单调递增栈的专项训练不

找到一个不错的[链接](https://leetcode.com/problems/sum-of-subarray-minimums/discuss/178876/stack-solution-with-very-detailed-explanation-step-by-step)，上面有解释和对应的题目。

Start with the linked LeetCode explanation for the monotonic-increasing-stack topic, then inspect how existing exercises are organized in the repository; no specific files or tests are named. Done means adding a focused exercise for this topic and its corresponding problem in the repository’s established format.

Vom Indexierungsmodell aus dem Issue-Text verfasst.