Update classification_of_data_structure.md

[Phoenix0415]

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• I've tested the code and ensured the outputs are the same as the outputs of reference code.
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[yuelinxin]

Hi there, than you for your PR. This PR is duplicate with #1005, can you check if it has the same changes, if not we can merge your PR after #1005.

[Phoenix0415]

hi, Thank you for your feedback. I added the term "层级结构" to provide a more detailed description.

here's what changed in my PR:
"树形结构和网状结构" -> "树形结构(或层级结构)和网状结构"

#1005
"divided into tree structures and network structures"

I recommend merging my PR after #1005 if the changes are acceptable

[krahets]

Hi @Phoenix0415 , thanks for your PR!

树形结构 and 层级结构 are not equavilant. 层级结构 is more general than 树形结构. Specifically, in 层级结构, it is not required that each child-node should correspond to only one parent-node.

[Phoenix0415]

uh, I see.
thanks for your explanation and clarification!