feat: solve No.342

Author: BaffinLee

301-400/342. Power of Four.md

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+# 342. Power of Four
+
+- Difficulty: Easy.
+- Related Topics: Math, Bit Manipulation, Recursion.
+- Similar Questions: Power of Two, Power of Three.
+
+## Problem
+
+Given an integer `n`, return **`true` if it is a power of four. Otherwise, return `false`**.
+
+An integer `n` is a power of four, if there exists an integer `x` such that `n == 4x`.
+
+ 
+Example 1:
+```
+Input: n = 16
+Output: true
+```Example 2:
+```
+Input: n = 5
+Output: false
+```Example 3:
+```
+Input: n = 1
+Output: true
+```
+ 
+**Constraints:**
+
+
+	
+- `-231 <= n <= 231 - 1`
+
+
+ 
+**Follow up:** Could you solve it without loops/recursion?
+
+## Solution
+
+```javascript
+/**
+ * @param {number} n
+ * @return {boolean}
+ */
+var isPowerOfFour = function(n) {
+    var num = 0b1010101010101010101010101010101;
+    return n > 0 && (n & (n - 1)) === 0 && (n & num) === n;
+};
+```
+
+**Explain:**
+
+nope.
+
+**Complexity:**
+
+* Time complexity : O(1).
+* Space complexity : O(1).