# [LeetCode] Power of Four 判断4的次方数

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

Example:
Given num = 16, return true.
Given num = 5, return false.

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

Credits:
Special thanks to @yukuairoy for adding this problem and creating all test cases.

```class Solution {
public:
bool isPowerOfFour(int num) {
while (num && (num % 4 == 0)) {
num /= 4;
}
return num == 1;
}
};```

```class Solution {
public:
bool isPowerOfFour(int num) {
return num > 0 && int(log10(num) / log10(4)) - log10(num) / log10(4) == 0;
}
};```

```class Solution {
public:
bool isPowerOfFour(int num) {
return num > 0 && !(num & (num - 1)) && (num & 0x55555555) == num;
}
};```

Power of Three

Power of Two

https://leetcode.com/discuss/97944/c-solution-using-bit-manipulation-with-one-line-code

LeetCode All in One 题目讲解汇总(持续更新中...)

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