【LeetCode 0231】【位运算】2的N次方

231. Power of Two

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 == 2^x.

Example 1:

**Input:** n = 1
**Output:** true
**Explanation: **2^0 = 1

Example 2:

**Input:** n = 16
**Output:** true
**Explanation: **2^4 = 16

Example 3:

**Input:** n = 3
**Output:** false

Constraints:

• -2^31 <= n <= 2^31 - 1

Follow up: Could you solve it without loops/recursion?

Idea

首先 2^n 不可能是0或者负数
其次 2^n 作为正数，其二进制位有且只有一个位是1

JavaScript Solution

/**
 * @param {number} n
 * @return {boolean}
 */
var isPowerOfTwo = function(n) {
    return !(n<=0) && !(n&(n-1))
};