How should I practice Resumable List Iterator?

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Problem · Array

Resumable List Iterator

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xAIFULLTIMEPHONE SCREEN

Problem statement

Design a finite iterator over an integer array whose progress can be saved and restored.

Iterator Behavior

Return the next value and signal exhaustion after the final value.
getState() returns a serializable, opaque state representing the current position.
setState(state) restores the iterator so that subsequent values are exactly the values that remained when the state was saved.

A caller must not assume that a state is an array index. A saved state must continue to work after the original iterator has advanced or become exhausted.

State Restoration

Save the iterator state before reading the first value and after every returned value, including the exhausted position. Restore a fresh iterator from each saved state, read it to exhaustion, and return all resulting suffixes in save order.

Row i of the returned int[][] contains all values returned after restoring the state saved after exactly i values had been consumed. The final row is empty because it represents the exhausted state.

Function

resumeSuffixes(values: int[]) → int[][]

Examples

Example 1

values = [4, 7, 9]return = [[4, 7, 9], [7, 9], [9], []]

The saved states represent the positions before 4, before 7, before 9, and after the iterator is exhausted. Restoring each state produces the corresponding suffix.