There are several guessing strategies, and points were awarded based off of how many guesses.

For $10\mathrm{\%}$ of the points, we make more than $110$ guesses. This could be achieved by making random guesses and stopping once we guess the correct answer.

For $20\mathrm{\%}$ of the points, we make more than $50$ guesses. This could be achieved by guessing each number from $-50$ to $50$.

For $30\mathrm{\%}$ of the points, we make more than $10$ guesses. This could be achieved by guessing numbers from $-50$ to $50$ at a certain interval, (say, $-50,-45,\dots ,45,50$) and checking individual numbers when close.

For $50\mathrm{\%}$ of the points, we make more than $3$ guesses. This could be achieved by performing a binary search.

For $75\mathrm{\%}$ of the points, we make $2$ guesses. This could be achieved by guessing $0$ and knowing that $N$ could either be $|N-0|$ or $-|N-0|$.

For $100\mathrm{\%}$ of the points, we make $1$ guess. We note that if we guess $50$, then the answer must be $50-|N-50|$, since the answer cannot be more than $50$. We could have done the same with $-50$ instead.

Time Complexity: $\mathcal{O}(1)$