Convert to Base -2 — LeetCode 1017 Python Solution

The problem

Given an integer n, return a binary string representing its representation in base -2. Note that the returned string should not have leading zeros unless the string is "0".

Example

Input

n = 2

Output

"110"

Python solution

class Solution:
    def baseNeg2(self, n: int) -> str:
        k = 1
        ans = []
        while n:
            if n % 2:
                ans.append('1')
                n -= k
            else:
                ans.append('0')
            n //= 2
            k *= -1
        return ''.join(ans[::-1]) or '0'

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 1017. Convert to Base -2 is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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