Prefix sum or for fixed range summation

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https://codeforces.com/problemset/problem/433/B
https://codeforces.com/problemset/problem/313/B

DP catagory solution where accumulate sum not possible in this kind of problem because of test cases and time limit.So if we do sum and insert it in an array previously,just use a vector and subtract from upper trange to lower range we'll get the answer.

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