Power of Two.

Author: recherst

Easy/231.Power of Two.playground/Contents.swift

@@ -0,0 +1,50 @@
+/**
+ Given an integer n, return true if it is a power of two. Otherwise, return false.
+
+ An integer n is a power of two, if there exists an integer x such that n == 2x.
+
+  
+
+ 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
+  
+
+ Constraints:
+ - -231 <= n <= 231 - 1
+  
+
+ Follow up: Could you solve it without loops/recursion?
+ */
+class Solution {
+    func isPowerOfTwo(_ n: Int) -> Bool {
+        if n <= 0  { return false }
+        var x = 0
+        while pow(2, pow: x) <= n {
+            x += 1
+        }
+        return pow(2, pow: x - 1) == n
+    }
+    
+    private func pow(_ base: Int, pow: Int) -> Int {
+        var res = 1
+        for _ in 0..<pow {
+            res *= base
+        }
+        return res
+    }
+}
+
+let s = Solution()
+let r = s.isPowerOfTwo(0)
+print(r)

Easy/231.Power of Two.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios' buildActiveScheme='true' importAppTypes='true'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Easy/231.Power of Two.playground/playground.xcworkspace/contents.xcworkspacedata

@@ -51,3 +51,4 @@
 49. [Implement Stack using Queues](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/225.Implement%20Stack%20using%20Queues.playground/Contents.swift)
 50. [Invert Binary Tree](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/226.Invert%20Binary%20Tree.playground/Contents.swift)
 51. [Summary Ranges](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/228.Summary%20Ranges.playground/Contents.swift)
+52. [Power of Two](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/231.Power%20of%20Two.playground/Contents.swift)