Merge the Nested Batches

Intermediate

A job returns results grouped into nested batches, but the next stage wants one flat sequence. Flatten the groups in order.

Implement `solve(List<List<Integer>> nested)` to return one flat list of all inner values in order.

Examples

Input[[1,2], [3], [4,5,6]]

Output[1, 2, 3, 4, 5, 6]

Input[[], [7]]

Output[7]

Hints

addAll appends an entire inner list at once.

Anonymous Apex

List<Integer> solve(List<List<Integer>> nested) {
    // flatten all inner values in order
    return null;
}

Your code runs in a secure sandbox against multiple hidden test cases. The problem is solved only when every test passes. Each run is isolated and any data changes are rolled back automatically.