Following is a way to sum the digits into a single digit.
e.g. let we have to sum the digits of number 234578.
2 + 3 + 4 + 5 + 7 + 8 = 29; sum it again until a single digit.
2 + 9 = 11; sum it again until a single digit.
1 + 1 = 2 ; it is final sum of digits.
so sum of digits of number 234578 is 2.
Here is the code for sum of digits:
For any given positive integers n;
if (n != 0) {
if (n % 9 == 0) {
return 9;
}
return n % 9;
}
return 0;
Piece of code will always return sum of digits.
One best way to find whether an integer is power of two or not :
For any given positive integer n;
return n & n - 1;
Expression will return:
zero; if n is power of 2,
non-zero; otherwise.
Best way to compare equality of two integer variables without using comparison operator is:
For any given integers a and b;
return a ^ b;
Expression will return:
zero; if a and b are equal,
non-zero; otherwise.
Two integer variables can be swapped in many different ways.
One of the best way to swap is given below.
For any given integers a and b;
a ^= b ^= a ^= b;
Raheel Shahzad who was my senior at Palmchip and the best Pakistani programmer I have seen so far on acm site, has asked how to make faster the following expression.
For any given integer n; n = n * 7;
I come up with the follwoing solution.
n = (n << 3) - n;
Limitation: n can overflow.
