Leetcode #693: Binary Number with Alternating Bits
In this guide, we solve Leetcode #693 Binary Number with Alternating Bits in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
Given a positive integer, check whether it has alternating bits: namely, if two adjacent bits will always have different values. Example 1: Input: n = 5 Output: true Explanation: The binary representation of 5 is: 101 Example 2: Input: n = 7 Output: false Explanation: The binary representation of 7 is: 111.
Quick Facts
- Difficulty: Easy
- Premium: No
- Tags: Bit Manipulation
Intuition
The problem structure lets us track state with bitwise operations.
Bit operations are constant time and avoid extra memory.
Approach
Apply XOR/AND/OR and shifts to maintain the required invariant.
Aggregate the result in a single pass.
Steps:
- Identify a bitwise invariant.
- Combine values with bit operations.
- Return the aggregated result.
Example
Input: n = 5
Output: true
Explanation: The binary representation of 5 is: 101
Python Solution
class Solution:
def hasAlternatingBits(self, n: int) -> bool:
prev = -1
while n:
curr = n & 1
if prev == curr:
return False
prev = curr
n >>= 1
return True
Complexity
The time complexity is O(n). The space complexity is O(1).
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.