How to find sum of elements from given index interval (i, j) in constant time?

Posted by Rajendra on Stack Overflow See other posts from Stack Overflow or by Rajendra
Published on 2010-03-18T20:23:02Z Indexed on 2010/03/18 20:31 UTC
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arrays

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interview-questions

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algorithm

Given an array. How can we find sum of elements in index interval (i, j) in constant time. You are allowed to use extra space.
Example:
A: 3 2 4 7 1 -2 8 0 -4 2 1 5 6 -1
length = 14

int getsum(int* arr, int i, int j, int len);
// suppose int array "arr" is initialized here
int sum = getsum(arr, 2, 5, 14);

sum should be 10 in constant time.

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