50. If the sum of the digits of a four-digit number added to the number itself equals 2017, then the four-digit number is . $\qquad$
Answer: 1994 or 2012.
Solution: Let the required four-digit number be $\overline{a b c d}$,
then
$$
a+b+c+d+\overline{a b c d}=2017,
$$

which means
$$
1001 a+101 b+11 c+2 d=2017,
$$

so
$a=1$ or 2.
(1) When $a=1$, $101 b+11 c+2 d=1016$, $b$ can only be $9, 11 c+2 d=107$, so $c=9, d=4$, the four-digit number is 1994.
(2) When $a=2$, $101 b+11 c+2 d=15$, obviously $b=0, 11 c+2 d=15$, so $c=1, d=2$, the four-digit number is 2012.

Therefore, the required numbers are 1994 or 2012.