MrDepomposition's blog

hello
By MrDepomposition, history, 4 years ago, In English

hello i am writing this blog because i asked a question but havent got asnwer for it, please explain me why do we need to use segment tree to calculate sums, why cant we just use c++ operator + (read more about this operator here — https://www.w3schools.com/cpp/cpp_operators.asp)

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4 years ago, # |
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I hope you're kidding

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4 years ago, # |
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The + operator in general won't give you the sum of an array over an index range [l...r] in log(N) time. A segment tree will.

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    4 years ago, # ^ |
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    yes but + operator is O(1) while segment tree is logN, so we should use + operator, isnt it?

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      4 years ago, # ^ |
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      Because you need to apply the + operator (r — l) = O(n) times to find the sum from l to r. With a segment tree, you can do this in O(log N)

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        4 years ago, # ^ |
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        r — l = n it means that r — l — n = 0 so the complexity is O(0), right?

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4 years ago, # |
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i am trying to solve this problem — https://codeforces.com/problemset/problem/409/H?locale=ru
but my segment tree solution fails

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4 years ago, # |
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Its big brain time!

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