Peeking iterator

Array Design Iterator

61.3% acceptance

Jan 13, 2026

1908

1052

Design an iterator that supports the peek operation on an existing iterator in addition to the hasNext and the next operations.

Solution

C++

Time O(1)

Space O(1)

LeetCode

solution.cpp

class PeekingIterator : public Iterator {
  int _next;
  bool _hasNext;
public:
  PeekingIterator(const vector<int>& nums) : Iterator(nums) {
    _hasNext = Iterator::hasNext();
    if (_hasNext) _next = Iterator::next();
  }

  int peek() {
    return _next;
  }

  int next() {
    int val = _next;
    _hasNext = Iterator::hasNext();
    if (_hasNext) _next = Iterator::next();
    return val;
  }

  bool hasNext() const {
    return _hasNext;
  }
};