Merge Three Sorted Arrays

You are given three integer arrays that are each sorted in non-decreasing order.
Merge the arrays into one sorted array and remove duplicate values. Return the merged array in non-decreasing order.

Function
mergeThreeSortedArrays(a: int[], b: int[], c: int[]) → int[]
Complete the function mergeThreeSortedArrays in the editor.
mergeThreeSortedArrays has the following parameters:
int a[]: the first sorted array
int b[]: the second sorted array
int c[]: the third sorted array
Returns int[]: the sorted merged array with duplicates removed

Examples
Example 1
a = [1, 3, 5]
b = [1, 2, 5, 6]
c = [2, 4, 6]
return = [1, 2, 3, 4, 5, 6]
After merging all values and removing duplicates, the sorted result is [1, 2, 3, 4, 5, 6].
Example 2
a = []
b = [0, 0, 1]
c = [1, 2]
return = [0, 1, 2]
Empty arrays are allowed. Duplicate 0 and 1 values are returned once.

Constraints
Each input array is sorted in non-decreasing order.
The arrays may contain duplicate values.
The arrays may be empty.

The trick is that sortedness does the work for you. Keep three pointers, one per array. Each step, take the smallest value among the pointers that are still in range. Append it only if it differs from the last value in the result, then advance every pointer sitting on that value. That gives O(n) time with no sorting and no hash set. The common pitfall is empty arrays, so guard every index check before you read. Another is dedupe against the wrong thing. Compare to the last appended element, not the previous input element. A lazy fallback is concatenating, sorting and deduping, which works but ignores the sorted input and may read as weak. If the pointer bookkeeping slips under pressure, StealthCoder is the hedge during the live OA, reading the problem and handing you a clean solution.

The honest play: practice the pattern, and have StealthCoder ready for the one you didn't see coming.