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Different Bits Sum Pairwise - InterviewBit Solution

Problem: Different Bits Sum Pairwise

Problem Description:

We define f(X, Y) as a number of different corresponding bits in the binary representation of X and Y. For example, f(2, 7) = 2, since binary representation of 2 and 7 are 010 and 111, respectively. The first and the third bit differ, so f(2, 7) = 2.

You are given an array of N positive integers, A1, A2,…, AN. Find the sum of f(Ai, Aj) for all pairs (i, j) such that 1 ≤ i, j ≤ N. Return the answer modulo 109+7.

For example,

A=[1, 3, 5]

We return

f(1, 1) + f(1, 3) + f(1, 5) + 
f(3, 1) + f(3, 3) + f(3, 5) +
f(5, 1) + f(5, 3) + f(5, 5) =

0 + 1 + 1 +
1 + 0 + 2 +
1 + 2 + 0 = 8

Solution Approach:

Solution in C++:

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