Given an integer array digits, return the total number of unique $3$ digit even numbers that can be formed using the elements in digits.

A valid $3$ digit even number must satisfy the following conditions:

• It contains exactly $3$ digits.

• It does not have a leading $0$.

• The integer formed is even.

• Each element in digits can be used at most as many times as it appears in the array.

Constraints:

• $3 \leq$ digits.length $\leq 10$

• $0 \leq$ digits[i] $\leq 9$

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