huzaifa242's blog

How to handle updates in DSU on trees
By huzaifa242, history, 5 years ago, In English

I read this Blog on DSU on trees.

Now, I have a doubt.

Given a tree with n nodes and each node has some color c[i], following query needs to be answered

1 x y: change color of node x to y

2 u c: count all the nodes with color c in subtree of u.

How to approach this??

Thanks for help in advance.

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5 years ago, # |
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Auto comment: topic has been updated by huzaifa242 (previous revision, new revision, compare).

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5 years ago, # |
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Do a preorder traversal/euler tour on the tree so that colors of nodes in the same subtree will be together. Now, you just need to keep a segment tree, with order statistic set in each node. I think that you can take it from here.

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5 years ago, # |
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actually u can solve this problem without a segment tree. Basically, u maintain n (of the n colors) binary search tree (seems difficult? Rmb pbds exits) in each of the BST, stores the order of the node in the euler tour. After that, a simple, lower_bound and upper_bound operation can solve the problem.

Memory: O(N), Time: O(N log N)

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    5 years ago, # ^ |
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    Thanks for this approach.

    But I wanted to know if something can be done using that blog?? I mean ca we handle updates using the technique mentioned in the blog??

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      5 years ago, # ^ |
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      I don't think so, cuz the result in each node is used by its ancestor

      Updating in this manner will be linear with a worst-case complexity of O(TN) where T is the number of updates

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