Python solution with detailed explanation


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    G

    Solution

    Power of Two https://leetcode.com/problems/power-of-two/

    Algorithm 1

    1. n & (n - 1) drops the** lowest set bit.** It's a neat little bit trick. https://discuss.leetcode.com/topic/20120/c-solution-n-n-1/2
      Let's use n = 00101100 as an example. This binary representation has three 1s.
    • If n = 00101100, then n - 1 = 00101011, so n & (n - 1) = 00101100 & 00101011 = 00101000. Count = 1.
    • If n = 00101000, then n - 1 = 00100111, so n & (n - 1) = 00101000 & 00100111 = 00100000. Count = 2.
    • If n = 00100000, then n - 1 = 00011111, so n & (n - 1) = 00100000 & 00011111 = 00000000. Count = 3.
    • n is now zero, so the while loop ends, and the final count (the numbers of set bits) is returned.
    • Test for power of two: (n & (n-1)) == 0
    class Solution(object):
        def isPowerOfTwo(self, n):
            """
            :type n: int
            :rtype: bool
            """
            if n <= 0:
                return False
            return (n & (n-1)) == 0
    

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