day 8

Author: sachuverma

Leetcode Daily Challenge/February-2021/08. Peeking Iterator.cpp

@@ -0,0 +1,71 @@
+/*
+Peeking Iterator
+===============
+
+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?
+
+
+Hint #1  
+Think of "looking ahead". You want to cache the next element.
+
+Hint #2  
+Is one variable sufficient? Why or why not?
+
+Hint #3  
+Test your design with call order of peek() before next() vs next() before peek().
+
+Hint #4  
+For a clean implementation, check out Google's guava library source code.
+*/
+
+/*
+ * Below is the interface for Iterator, which is already defined for you.
+ * **DO NOT** modify the interface for Iterator.
+ *
+ *  class Iterator {
+ *		struct Data;
+ * 		Data* data;
+ *		Iterator(const vector<int>& nums);
+ * 		Iterator(const Iterator& iter);
+ *
+ * 		// Returns the next element in the iteration.
+ *		int next();
+ *
+ *		// Returns true if the iteration has more elements.
+ *		bool hasNext() const;
+ *	};
+ */
+
+class PeekingIterator : public Iterator
+{
+public:
+  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.
+  }
+
+  // Returns the next element in the iteration without advancing the iterator.
+  int peek()
+  {
+    return Iterator(*this).next();
+  }
+
+  // hasNext() and next() should behave the same as in the Iterator interface.
+  // Override them if needed.
+  // 	int next() {
+  // 	}
+
+  // 	bool hasNext() const {
+  // 	}
+};

Leetcode Daily Challenge/February-2021/README.MD

@@ -8,6 +8,7 @@
 | 4.  | [Longest Harmonious Subsequence](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/584/week-1-february-1st-february-7th/3628/) | [cpp](./04.%20Longest%20Harmonious%20Subsequence.cpp) |
 | 5.  | [Simplify Path](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/584/week-1-february-1st-february-7th/3629/) | [cpp](./05.%20Simplify%20Path.cpp) |
 | 6.  | [Binary Tree Right Side View](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/584/week-1-february-1st-february-7th/3630/) | [cpp](./06.%20Binary%20Tree%20Right%20Side%20View.cpp) |
-| 7.  | [Shortest Distance to a Character](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/584/week-1-february-1st-february-7th/3631/) | [cpp](./07.%20Shortest%20Distance%20to%20a%20Character.cpp) |
+| 7.  | [Shortest Distance to a Character](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/584/week-1-february-1st-february-7th/3631/) | [cpp](./07.%20Shortest%20Distance%20to%20a%20Character.cpp) | 
+| 8.  | [Peeking Iterator]() | [cpp](./08.%20Peeking%20Iterator.cpp) |