# 342 Power of Four

### Problem:

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?

### Solution:

``````public class Solution {
public boolean isPowerOfFour(int num) {
if (num <= 0) {
return false;
}
while (num > 3) {
if (num % 4 != 0) {
return false;
}
num = num / 4;
}
return num == 1;
}
}
``````
``````public class Solution {
public boolean isPowerOfFour(int num) {
return num == 1 || num == 4 || num == 16 || num == 64 || num == 256 || num == 1024 || num == 4096 || num == 16384 || num == 65536 || num == 262144 || num == 1048576 || num == 4194304 || num == 16777216 || num == 67108864 || num == 268435456 || num == 1073741824;
}
}
``````
``````public class Solution {
public boolean isPowerOfFour(int num) {
int count0=0;
int count1=0;

while(num>0){
if((num&1)==1){
count1++;
}else{
count0++;
}

num>>=1;
}

return count1==1 && (count0%2==0);
}
}
``````
``````public class Solution {
public boolean isPowerOfFour(int num) {
if (num <= 0) {
return false;
}
double res = Math.log10(num) / Math.log10(4);
return Double.compare(res, (int)res) == 0;
}
}
``````
``````public class Solution {
public boolean isPowerOfFour(int num) {
return num > 0 && (num & (num - 1)) ==0  && (num & 0x55555555) == num;
}
}
``````