Problem

Difficulty: Easy
Tags: Math, Recursion

Intuition

I believed that there won’t be that much power of threes in the range of integer, so I just listed them. i copied from the discussion board, but that was exactly what I was trying to do.

Approach

compare the number with all the possible power of threes.

Solution

bool isPowerOfThree(int n) {
    return n == 1 || n == 3 || n == 9 || n == 27 || n == 81 || n == 243 || n == 729 || n == 2187 || n == 6561 || n == 19683 || n == 59049 || n == 177147 || n == 531441 || n == 1594323 || n == 4782969 || n == 14348907 || n == 43046721 || n == 129140163 || n == 387420489 || n == 1162261467 || n == 3486784401 || n == 10460353203 || n == 31381059609 || n == 94143178827 || n == 282429536481 || n == 847288609443 || n == 2541865828329 || n == 7625597484987 || n == 22876792454961 || n == 68630377364883 || n == 205891132094649 || n == 617673396283947 || n == 1853020188851841 || n == 5559060566555523 || n == 16677181699666568 || n == 50031545098999710 || n == 150094635296999140 || n == 450283905890997400 || n == 1350851717672992000 || n == 4052555153018976000 ;
}

thougths

this was interesting question, but there wasn’t anything to learn.

Complexity

Time: $O(1)$
Space: $O(1)$