Which of the following functions is a one$-$to$-$one correspondence?

$f$:$RR,$ where $f(x)=x+5$

$f$:$ZZ,$ where $f(n)=7$

$f$:$RR,$ where $f(x)=3x^2+6$

f: $ZZ,$ where $f(n)=|n|-3$