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Today I spent some time on practicing coding. When I was trying to solve a problem about finding paths with elements whose sum equals to a specified value, given a binary tree and a value, I stumble against some unknown problems.
As I firstly finished my code, I got a null result. My codes at beginning are like this.
Can you guys find where the problem lies?
Actually, the problem happens when I was trying to append a path to the res list followed by pop operation. You may better understand with the example below.
I bet now you must realize the appending here is about passing by reference. What is appended to the list
a is just a reference of list b. When you modify the b, the corresponding content in a will also change.In this way, I have to reassign another list and copy the content from b to this list. That is
Finally, I got the correct answer.
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