7. (3 points) Three piles of balls have a total of 2012 balls. If the same number of balls is taken from each pile, the second pile will have 17 balls left, and the number of balls left in the first pile is twice the number of balls left in the third pile. How many balls were originally in the third pile? $\qquad$ 

 untranslated part: 颗小球. 

Note: The untranslated part "颗小球." is a placeholder for the answer and should be replaced with the numerical answer in the final solution. In English, it would be "balls."
【Analysis】Let $x$ be the number taken away, and $y$ be the number left in the third pile, then: $x+2 y+(x+17)+(x+y)=2012$, then $3 x+3 y+17$ $=2012$, and then organize to get: $3(x+y)=1995$, and further find the value of $x+y$, which is the number of balls in the third pile.

【Solution】Solution: Let $x$ be the number taken away, and $y$ be the number left in the third pile,
then: $\square$
$$
\begin{aligned}
x+2 y+(x+17)+(x+y) & =2012 \\
3 x+3 y+17 & =2012 \\
3(x+y) & =1995 \\
3(x+y) \div 3 & =1995 \div 3 \\
x+y & =665
\end{aligned}
$$

Answer: The third pile has 665 balls;
Therefore, the answer is: 665.