Li Lei and Han Meimei have different opinions regarding the linear time complexity in the video lecture.对于视频中线性递归的时间复杂度，A、B两位同学有不同的看法。Li Lei aggrees to the video, the complexity is O(n) because there are n instances each requiring O(1) execution time. A同学赞同视频中的算法，由于单个递归实例需要O（1）时间完成，共有n个实例，所以整个算法的复杂度是O（n）。However, Han Meimei believes the time for sum（A,n) to be O(n) instead of O(1), since it's still executing even when calling sum(A,n-1), leading to a total time complexity of $n+n-1+...+3+2+1=O（{n}^{2}$. You agree with 但B同学认为，当sum（A,n）函数中调用sum(A,n-1)时，sum(A,n)仍在执行，因此sum（A,n）的完成时间不是O(1)而是O（n），依此计算，整个算法的复杂度应该为$n+n-1+...+3+2+1=O（{n}^{2}）。$请问哪位同学对了？