K Smallest Elements from Sorted Arrays

You are given an array of integer arrays arrays. Each inner array is sorted in nondecreasing order. Return the k smallest values across all inner arrays in nondecreasing order.
Duplicate values occupy separate positions and must be retained. An empty inner array contributes no values. When k is zero, return an empty array.
Do not insert every input value into a heap. Maintain at most one current candidate from each nonempty inner array.

Function
kSmallestElements(arrays: int[][], k: int) → int[]

Examples
Example 1
arrays = [[1,4,7],[2,5],[3,6,9]]
k = 5
return = [1,2,3,4,5]
The first five values in the merged order are 1, 2, 3, 4, 5.
Example 2
arrays = [[],[-3,-1,2],[-3,4]]
k = 4
return = [-3,-3,-1,2]
Both occurrences of -3 are retained, and the empty array is ignored.

Constraints
1 <= arrays.length <= 10000
0 <= arrays[i].length
The total number of values across all arrays is at most 200000.
Each inner array is sorted in nondecreasing order.
-2147483648 <= arrays[i][j] <= 2147483647
0 <= k <= the total number of values.

The trick is a min-heap seeded with the first element of each nonempty array. Store (value, arrayIndex, elementIndex) in each entry. Pop the smallest, append it to the result, then push the next element from the same array if one exists. Repeat until you have k values or the heap empties. That costs O(n + k log m), where m is the number of arrays and n is the total value count. The common pitfalls are all edge cases. k equals zero should return an empty array immediately. Empty inner arrays must be skipped at seed time. Duplicates stay, so don't dedupe. Values hit the full 32-bit range, so don't use a sentinel like Integer.MAX_VALUE, and be careful with subtraction in comparators because it overflows. If the heap logic gets tangled mid-assessment, StealthCoder is the hedge that hands you the clean version.

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