leetcode 371. Sum of Two Integers bitwise operations python3

I. Description of the problem

Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -.

Example 1:

Input: a = 1, b = 2
Output: 3

Example 2:

Input: a = -2, b = 3
Output: 1

II. Problem-solving ideas

This question is if you do not have a similar sum ([a, b] such a tricky operation, but truly a local topic and want to visit, you'll find that this question is still a little something.

This question requires an understanding of the underlying computing computer.

When computer numerical calculation in the bottom are a number of first complement representation, and then converted to the source code After computing the return.

Specifically related can refer to this blog.

https://blog.csdn.net/u011240016/article/details/52433355

The most important point is this:

Adder:
Integer: [A] Complement + [B] Complement = [A + B] Complement (mod 2 ^ (n + 1 ))
Decimal: [A] Complement + [B] Complement = [A + B] Complement (mod 2)

Subtraction:
Integer: [AB] Complement = [A] Complement + [-B] Complement (mod 2 ^ (n + 1 ))
Decimal: [AB] Complement = [A] Complement + [-B] Complement (mod 2)
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Understood by complement, subtraction is actually addition.

So we just need to implement additions.

It is an addition, phase two numbers to get into position where it is needed,

The two numbers above would like to add a carry results then want to add, the same method of calculating the carry,

Until carry zero.

There are two points where noted:

1.python unlike C ++ Java, the trouble is that in fact there is no numerical limit of the median, worse is the subject did not give number range, based on C ++ situation there should be a 32-bit integer.

2. If the carry note exceeds the 32-bit value overflows description, taken out.

More leetcode algorithm problem solution: Columns  leetcode algorithm from zero to the end

III. Source

Reference Code: https://leetcode.com/problems/sum-of-two-integers/discuss/400375/python-methods-%3A-easy-to-understand

class Solution:
    #47
    def getSum(self, a: int, b: int) -> int:
        
	
        # Prevent negative number
        while b & 0xffffffff: # b & 0xffffffff will remain the same as b with 32 bit 
            c = a & b
            a = a ^ b
            b = c << 1
        
        return a & 0xffffffff if b > 0xffffffff else a