boolean isPowerOf2(int x) { while (((x % 2) == 0) && x > 1) { x /= 2; } return (x == 1); }

A lot nicer solution is the one using bit operation:

boolean isPowerOf2(int x) { return x > 0 && (x & (x - 1)) == 0; }

Here the idea is that every number that is a power of 2 has exactly one bit set to 1 in its binary representation and if you subtract 1 from this number you get a number where all first bits (starting from right) are 1 in the binary representation:

2 = 00000010 2 - 1 = 1 = 00000001 4 = 00000100 4 - 1 = 3 = 00000011 8 = 00001000 8 - 1 = 7 = 00000111 16 = 00010000 16 - 1 = 15 = 00001111 ...And if you do a bitwise AND (operator '&') on the original number and the original number subtracted by 1, we get 0:

2 & 1 = 00000010 & 00000001 = 0 4 & 3 = 00000100 & 00000011 = 0 8 & 7 = 00001000 & 00000111 = 0 16 & 15 = 00010000 & 00001111 = 0 ...

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