Practice Peeking Iterator

Read the task, work through the examples, and check your approach against the constraints. Use the original LeetCode task for coding and submissions.

Medium#284

LeetCode Problem

Peeking Iterator

Array Design Iterator

Problem Statement

PeekingIterator wraps an existing integer iterator. next() consumes and returns the next value; hasNext() reports whether one remains; peek() returns the next value without consuming it. next and peek are invoked only when valid. Practice approach: Buffer one upcoming value and track its presence separately. peek fills the buffer only if empty; next consumes the buffer before delegating to the underlying iterator. Repeated peeks must return the same value. The wrapper uses O(1) extra space and adds O(1) work per call. A separate presence flag also permits generic values without reserving a sentinel.

Source: Peeking Iterator on LeetCode. Use the original task for its coding environment and submissions.

Examples

# Example 1

Input

["PeekingIterator","peek","peek","next","hasNext","next","hasNext"]
[[[4,7]],[],[],[],[],[],[]]

Output

[null,4,4,4,true,7,false]

Explanation

Two peeks leave 4 unconsumed; only next advances the underlying sequence.

Constraints

1 <= nums.length <= 1000

1 <= nums[i] <= 1000

At most 1000 total method calls.

next and peek calls are valid.

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