Given two integers a and b, return the sum of the two integers without using the operators + and -.
We cannot use arithmetic operators, so we have to use bit manipulation to achieve addition.
The XOR operator is useful for bit manipulation where its output is shown below.
1^1=0 0^0=0 0^1=1
From the code above we observe that 1^1=0 which is not equal to 1+1. We can use the AND(&) operator to handle carry to calculate the correct answer. We shift the carry to the left and repeat the operations until we get a result of 0 meaning there are no more carries.
Here is an example:
def getSum(self, a: int, b: int) -> int: while (b != 0): carry = a & b a = a ^ b b = carry << 1 return a
The time complexity is 0(n).
The solution is sufficient for most scenarios but we can improve it by consider that the range of bits for representing a value is not 32 in Python.
Therefore, we have to use a 32 bit mask of 1's represented by 0xfffffff.
The mask expands a number into a 32 bit / unsigned integer.
Our solution becomes:
def getSum(self, a: int, b: int) -> int: mask = 0xffffffff while (b & mask) > 0: carry = (a & b) << 1 a = (a ^ b) b = carry return (a & mask) if b > 0 else a
We can use logarithms to achieve the same result.
From our knowledge of logarithms, we know that
def getSum(self, a: int, b: int) -> int: return int(math.log2(pow(2,a)*pow(2,b)))
Top comments (4)
A friend of mine and I tried writing some simple functions in python without using any arithmetic operators or numeric literals. It was pretty fun, mostly boiled down to taking the length of lists of empty lists and other objectively cursed things. It was still a fun exercise though and definitely worth trying. I like your approach of using logic operators, although it still seems a little too close to normal addition to me. The log method was really neat and definitely not something I would have thought of.
try to make a catchy title, to gain traffic:
instead of Sum of Two Integers,
Sum of Two Integers ( without + operator )
Yes, the title is kinda misleading (if it makes you think it is just simply adding numbers). This could be made more interesting.
Thanks for the suggestion.