The output $y[n]$ of a discrete-time system for an input $x[n]$ is
$$y\left [ n \right ]=\underset{-\infty \leq k\leq n}{\text{max}} \mid x\left [ k \right ] \mid$$
The unit impulse response of the system is
- $0$ for all $n$.
- $1$ for all $n$.
- unit step signal $u\left [ n \right ].$
- unit impulse signal $\delta \left [ n \right ].$