Impression of Week 9

The biggest challenge we have for this week is the second term test. My strategy for the test was going through all the lecture slides since the first term tests. Also, I redid all the labs and quiz again. I don't know how well have I done for the test, because after the test, I've run the code I wrote on python, and it doesn't work the way as I expected during the test; I just looking for as many partial marks as possible for that questions.

Due to the test, we didn't talk too much about new materials except for delete algorithm for BTNode. This is quite complex since it involves many cases. First, if the targeted item is a nodes with no children( leaves), or the nodes with children. The point of deleting a parental node is that once you delete it, the structure of the node has been changed. For example,

we can see, when 4 is been deleted, not only was it removed, but also did its children node become a parental node and replaced the old node's position. One thing to keep in the mind is that we always move the left side nodes up to replace the former parental nodes. Why? Due to the definition of BTNode, we always want the smaller value on the left side while greater value on the other. So when we making a new node, we have to make sure that, once the new node has been placed, its right side is larger than its own value.

Here is my thoughts of thinking how the code actaully works for the above examples(please correct me if I'm wrong):

We want to delete 4, and, node is not None, and  4 is smaller than 8, so we going to left side by applying delete function recursively on the left side. This time, the node value is equal to target value 4. At same time, neither its left nor right is None. So we going to else part.

In the part, first, we want to know its left side's biggest value, and we know it must be 2, so we replace value 4 as value 2. But we still have its left side value 2 exists and we need to delete it.

So we applying delete function recursively again to its left side and changing the target_delete value from 4 to 2.

And this time we going to third elif part. We know that value 2's right is None and left is None, so we return its left which is  None, and this None has been assgined to value 2's left.

So we delete value 4, and at same time, we move up the value 2 to its supposed position