Today I have done leetcode's April LeetCoding Challenge with cpp.

April LeetCoding Challenge 25

Description

Peeking Iterator

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

Implement the PeekingIterator class:

• PeekingIterator(Iterator<int> nums) Initializes the object with the given integer iterator iterator.
• int next() Returns the next element in the array and moves the pointer to the next element.
• boolean hasNext() Returns true if there are still elements in the array.
• int peek() Returns the next element in the array without moving the pointer.

Note: Each language may have a different implementation of the constructor and Iterator, but they all support the int next() and boolean hasNext() functions.

Example 1:

Input
["PeekingIterator", "next", "peek", "next", "next", "hasNext"]
[[[1, 2, 3]], [], [], [], [], []]
Output
[null, 1, 2, 2, 3, false]

Explanation
PeekingIterator peekingIterator = new PeekingIterator([1, 2, 3]); // [1,2,3]
peekingIterator.next();    // return 1, the pointer moves to the next element [1,2,3].
peekingIterator.peek();    // return 2, the pointer does not move [1,2,3].
peekingIterator.next();    // return 2, the pointer moves to the next element [1,2,3]
peekingIterator.next();    // return 3, the pointer moves to the next element [1,2,3]
peekingIterator.hasNext(); // return False

Constraints:

• 1 <= nums.length <= 1000
• 1 <= nums[i] <= 1000
• All the calls to next and peek are valid.
• At most 1000 calls will be made to next, hasNext, and peek.

Follow up: How would you extend your design to be generic and work with all types, not just integer?

Solution

class PeekingIterator : public Iterator {
  int num;
  bool has;
public:
	PeekingIterator(const vector<int>& nums) : Iterator(nums) {
      has = Iterator::hasNext();
      if(has) num = Iterator::next();
    }
	
    // Returns the next element in the iteration without advancing the iterator.
	int peek() {
      return num;
	}
	
	// hasNext() and next() should behave the same as in the Iterator interface.
	// Override them if needed.
	int next() {
    int cur = num;
    has = Iterator::hasNext();
    if(has) num = Iterator::next();
    return cur;
	}
	
  bool hasNext() const {
    return has;
  }
};

// Accepted
// 14/14 cases passed (4 ms)
// Your runtime beats 59.03 % of cpp submissions
// Your memory usage beats 72 % of cpp submissions (7.5 MB)