Create 231_Power_of_Two.md

Author: koji

231_Power_of_Two.md

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+## 231. Power of Two
+
+Given an integer n, write a function to determine if it is a power of two.
+
+ 
+
+Example 1:
+
+Input: n = 1
+Output: true
+Explanation: 20 = 1
+Example 2:
+
+Input: n = 16
+Output: true
+Explanation: 24 = 16
+Example 3:
+
+Input: n = 3
+Output: false
+Example 4:
+
+Input: n = 4
+Output: true
+Example 5:
+
+Input: n = 5
+Output: false
+ 
+
+Constraints:
+
+-231 <= n <= 231 - 1
+
+```python
+def isPowerOfTwo(self, n: int) -> bool:
+ # return n > 0 and n == n & -n
+ if not n or n < 1: return False
+ return n == n & (-n)
+```
+
+```
+Runtime: 24 ms, faster than 95.06% of Python3 online submissions for Power of Two.
+Memory Usage: 14.1 MB, less than 99.94% of Python3 online submissions for Power of Two.
+```