Closest integer

Given an integer, find the closest integer with the same weight. Here weight is defined as the count of set bits in the decimal representation of the integer.

Example

# 0111 => 1011
closest_integer(7) #=> 11:

Code

def closest_integer(num)
    for i in 0..64
        # Check if consecutive bits are different
        if (x >> i) & 1 ^ (x >> x+1) & 1 == 1
            # then swap them or flip their bits
            mask = 1 << i | 1 << i+1
            x = x ^ mask
            return x
        end
    end

    raise Exception('All bits are 0 or 1')

end

Complexity

Time: O(n) where n is the number of bits in the given integer (max # of bits)