Create 284-peeking_iterator.py

Author: stevestar888

284-peeking_iterator.py

@@ -0,0 +1,87 @@
+"""
+https://leetcode.com/problems/peeking-iterator/
+
+Strat:
+    Store (cache) the next element we should return, along with if
+    we have an additional element to return. Have to ensure we turn
+    our iterator into 
+
+Stats: O(n) / linear time, O(n) / linear space
+    Runtime: 16 ms, faster than 94.98% of Python online submissions for Peeking Iterator.
+    Memory Usage: 12.7 MB, less than 93.31% of Python online submissions for Peeking Iterator.
+    
+Clean solution by Stefan: https://leetcode.com/problems/peeking-iterator/discuss/72557/NexthasNext-use-peek
+"""
+class PeekingIterator(object):
+    def __init__(self, iterator):
+        """
+        Initialize your data structure here.
+        :type iterator: Iterator
+        """
+        #make our vars accessible within whole class by using self
+        self.iterator = iterator
+        
+        #try to init our vars used for caching
+        if self.iterator.hasNext():
+            self.cached_has_next = True
+            self.cached_next = iterator.next()
+        else:
+            self.cached_has_next = False
+        
+
+    def peek(self):
+        """
+        Returns the next element in the iteration without advancing the iterator.
+        :rtype: int
+        """
+        return self.cached_next
+        
+
+    def next(self):
+        """
+        :rtype: int
+        """
+        tmp = self.cached_next
+        
+        #see if we can call next() again
+        if self.iterator.hasNext():
+            #update cached_next with new element
+            self.cached_next = self.iterator.next()
+        else:
+            self.cached_has_next = False
+        
+        #return the prev elem which was stored in tmp
+        return tmp
+        
+
+    def hasNext(self):
+        """
+        :rtype: bool
+        """
+        return self.cached_has_next
+        
+
+# class Iterator(object):
+#     def __init__(self, nums):
+#         """
+#         Initializes an iterator object to the beginning of a list.
+#         :type nums: List[int]
+#         """
+#
+#     def hasNext(self):
+#         """
+#         Returns true if the iteration has more elements.
+#         :rtype: bool
+#         """
+#
+#     def next(self):
+#         """
+#         Returns the next element in the iteration.
+#         :rtype: int
+#         """
+
+# Your PeekingIterator object will be instantiated and called as such:
+# iter = PeekingIterator(Iterator(nums))
+# while iter.hasNext():
+#     val = iter.peek()   # Get the next element but not advance the iterator.
+#     iter.next()         # Should return the same value as [val].