The shortest distance between the line $x - y = 1$ and the curve $x ^ { 2 } = 2 y$ is:\\ (1) $\frac { 1 } { 2 }$\\ (2) $\frac { 1 } { \sqrt { 2 } }$\\ (3) $\frac { 1 } { 2 \sqrt { 2 } }$\\ (4) 0