kgargdun's blog

By kgargdun, history, 5 months ago, In English

Hi, I am on my adventure to solve CSES problem set. I found this nice editorial for Range Query section here

But i guess some new problems were added or were skipped there. I am struggling in one such problem. here Any hint/approach will be highly appreciated!

EDIT: Yay AC ! I tried to code it as simple as possible.

AC solution
 
 
 
 
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5 months ago, # |
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The main challenge with the problem is finding $$$cost(i) = \min\limits_{1 \leq j \leq n}(p_j + |i-j|)$$$ quickly

We can split the cost into two parts: $$$cost(i) = \min(p_j + (i - j))$$$ when $$$j \leq i$$$ and $$$cost(i) = \min(p_j + (j - i))$$$ when $$$j \geq i$$$

Combining them together, we get $$$cost(i) = \min(\min\limits_{1 \leq j \leq i} (p_j - j) + i, \min\limits_{i \leq j \leq n}(p_j + j) - i)$$$

We can use two point-update, range-minimum-query segment trees to achieve this. One stores $$$p_i - i$$$ and the other stores $$$p_i + i$$$.

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

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5 months ago, # |
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Still, there is a bug

            lli left = query(arr, tree2, 0, n-1, **1**, a-1, 1);

should be replaced with

            lli left = query(arr, tree2, 0, n-1, **0**, a-1, 1);