Which of the following function is not Riemann Integrable on [0, 1] ?
1
\(\rm f(x)= \begin{cases}1 & \text { if } x \in \mathbb{Q} \cap[0,1] \\ -1 & \text { otherwise }\end{cases} \)
2
\(\rm f(x)= \begin{cases}x & \text { if } x \in[0,1) \\ 0 & \text { if } x=1\end{cases} \)
3
\(\rm f(x)=\displaystyle\int_0^x\left|\frac{1}{2}-t\right| d t \)
4
\(\rm f(x)= \begin{cases}x^2 \sin (1 / x) & \text { if } x \neq 0 \\ 0 & \text { if } x=0\end{cases} \)