How should I practice Stepped Iterator?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Bridge phone screen problems in FastPrep.

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FastPrep tags this as a Bridge phone screen coding practice problem when the problem catalog has that company and stage context.

Problem · Array

Stepped Iterator

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● Easy

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Problem statement

Simulate a stepped iterator over the integer array values for the ordered operation sequence operations. Return one string result for every operation, in the same order.

For a positive step, the iterator starts before the first element and its next zero-based index is step - 1. Process each operation as follows:

HAS_NEXT returns "true" when the next index is inside values, or "false" otherwise. It never changes the iterator state.
NEXT returns the integer at the next index as a decimal string, then advances the next index by step.
An exhausted NEXT returns "ERROR_EXHAUSTED" and leaves the state unchanged.
An operation other than HAS_NEXT or NEXT returns "ERROR_INVALID_OPERATION" and leaves the state unchanged.

If step is not positive, every operation returns "ERROR_INVALID_STEP" and no iterator state is created.

Function

runSteppedIterator(values: int[], step: int, operations: String[]) → String[]

Examples

Example 1

values = [1,2,3,4,5,6]step = 2operations = ["NEXT","NEXT","NEXT"]return = ["2","4","6"]

The successive next positions are 2, 4, and 6 in one-based order, so the three NEXT operations emit 2, 4, and 6.

Example 2

values = [10,20,30,40,50]step = 3operations = ["HAS_NEXT","NEXT","HAS_NEXT","NEXT","HAS_NEXT"]return = ["true","30","false","ERROR_EXHAUSTED","false"]

The first HAS_NEXT is true and NEXT emits 30. The next stepped position is outside the array, so later checks are false and the exhausted NEXT reports its error without changing state.

Example 3

values = [7,8]step = 1operations = ["UNKNOWN","HAS_NEXT","NEXT"]return = ["ERROR_INVALID_OPERATION","true","7"]

The unknown operation reports an error without moving the iterator. The following HAS_NEXT remains true, and NEXT still emits the first value.

Example 4

values = [7,8]step = 0operations = ["HAS_NEXT","NEXT"]return = ["ERROR_INVALID_STEP","ERROR_INVALID_STEP"]

A non-positive step is invalid at initialization, so every requested operation receives the deterministic invalid-step result.

Constraints

0 <= values.length.
Values less than or equal to 0 for step follow the invalid-step rule.
0 <= operations.length, and every operation is a non-null string.