Blog # 53 : How to multiply by 7?

Give a fast method to multiply a number by 7. Click here to see the solution. p.s. - For Remarks please hit the given link once. For Hint, hit it twice and for the solution, hit it thrice. Courtesy: Vibhaj Remarks: Remember when you were studying maths in junior high-school Hints: In how many ways can you multiply a number by 7? Solution: We multiply by 7 by first multiplying by 8 and subtracting the number from the result. Multiplication by 8 is equivalent to shifting left 3 bits. Complexity: Time : O(1) Space : O(1) Code: int multiply_7(int N){ return (N << 3) - N; }