oversolver's blog

Efficient solution to add / sum problem
By oversolver, history, 6 years ago, In English

We have n points (xi, yi). Let both x and y be different and from [1, n].

Initially, all points have zero value.

Two types of queries:

1) add X — adding +1 to all points with xi ≤ X

2) sum Y — calculate sum of values of points with yi ≤ Y

What is best known solution? (Problem not from running contest).

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6 years ago, # |
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With square Root Decomposition we can have updates and queries in .

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6 years ago, # |
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You can do sqrt decomposition on either queries or divide in sqrt blocks by y-value, and in each block keep sorted by x value. Both solutions lead to sqrt*log complexity, but since you've asked for best known solution, I think you've already tried these.

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6 years ago, # |
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Sort by Y, divide into K blocks, precalc number of points <= X for each block. For each block keep sum of all the points in this block, so updates will be processed in O(K). Queries for sum of complete block will give also O(K), and to process incomplete block you can store just one global Fenwick tree by X, so total time for sum query will be .

That gives per query with

If you will add sqrt decomposition on queries instead of Fenwick, you will get per query.

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6 years ago, # |
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Is it an amazing coincidence that a similar problem shows up in the contest today. Take a look at 1093E - Intersection of Permutations.

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