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Give a fast way to multiply a number by 7.
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(12 votes, avg: 2.67)
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Give a fast way to multiply a number by 7.
5,802 Views | (12 votes, avg: 2.67)
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n<<3 - n = 7n
N<<3+N=7N
this will work only for integers !!
what about doubles , floats ????
deep,
If interviewer asks you to do this for float or doubles.. you need to say “there is no way except ‘7*N’ “.
Hope you are happy now.
Just a correction :
N
Give a fast way to multiply a number by n.
deep,
Depending on the architecture and instruction timings, something like
const double A = N+N;
result = (A+A)+(A+N);
might be faster (4 additions, and maybe two of them can run in parallel) than just doing
result = N*7.0;
7N = N
Assuming binary numbers,
7 can be broken down as (4 + 2 + 1)
So the multiplication with x becomes
x*(4+2+1) giving x*4 + x*2 + x
Using shift operations and addition, multiplication should be faster.
I’m not sure about the correctness of this answer though.
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