342. Power of Four

342. Power of Four (Easy)

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.

Example 1:

Input: 16
Output: true

Example 2:

Input: 5
Output: false

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

Related Topics:
Bit Manipulation

Similar Questions:

• Power of Two (Easy)
• Power of Three (Easy)

Solution 1.

// OJ: https://leetcode.com/problems/power-of-four/
// Author: github.com/lzl124631x
// Time: O(1)
// Space: O(1)
class Solution {
public:
    bool isPowerOfFour(int num) {
        return __builtin_popcount(num) == 1 && ((~0x55555555 & num) == 0);
    }
};

Or

// OJ: https://leetcode.com/problems/power-of-four/
// Author: github.com/lzl124631x
// Time: O(1)
// Space: O(1)
class Solution {
public:
    bool isPowerOfFour(int num) {
        return num != INT_MIN && !(num & (num - 1)) && (num & 0x55555555);
    }
};