284.peeking-iterator.cpp

/*
 * @lc app=leetcode id=284 lang=cpp
 *
 * [284] Peeking Iterator
 *
 * https://leetcode.com/problems/peeking-iterator/description/
 *
 * algorithms
 * Medium (40.96%)
 * Total Accepted:    77.3K
 * Total Submissions: 188.7K
 * Testcase Example:  '["PeekingIterator","next","peek","next","next","hasNext"]\n[[[1,2,3]],[],[],[],[],[]]'
 *
 * Given an Iterator class interface with methods: next() and hasNext(), design
 * and implement a PeekingIterator that support the peek() operation -- it
 * essentially peek() at the element that will be returned by the next call to
 * next().
 * 
 * Example:
 * 
 * 
 * Assume that the iterator is initialized to the beginning of the list:
 * [1,2,3].
 * 
 * Call next() gets you 1, the first element in the list.
 * Now you call peek() and it returns 2, the next element. Calling next() after
 * that still return 2. 
 * You call next() the final time and it returns 3, the last element. 
 * Calling hasNext() after that should return false.
 * 
 * 
 * Follow up: How would you extend your design to be generic and work with all
 * types, not just integer?
 * 
 */
// Below is the interface for Iterator, which is already defined for you.
// **DO NOT** modify the interface for Iterator.
#include<bits/stdc++.h>
using namespace std;

class Iterator {
    struct Data;
	Data* data;
public:
	explicit Iterator(const vector<int>& nums);
	explicit Iterator(const Iterator& iter);
	virtual ~Iterator();
	// Returns the next element in the iteration.
	int next();
	// Returns true if the iteration has more elements.
	bool hasNext() const;
};


class PeekingIterator : public Iterator {
private:
	int i;
	vector<int> nums;
public:
	explicit PeekingIterator(const vector<int>& nums) : Iterator(nums) {
	    // Initialize any member here.
	    // **DO NOT** save a copy of nums and manipulate it directly.
	    // You should only use the Iterator interface methods.
	    this->nums = nums;
	    i = 0;
	}

    // Returns the next element in the iteration without advancing the iterator.
	int peek() {
        return nums[i];
	}

	// hasNext() and next() should behave the same as in the Iterator interface.
	// Override them if needed.
	int next() {
	    return nums[i++];
	}

	bool hasNext() const {
	    return i<nums.size();
	}
};