solve problem Peeking Iterator

Author: P-ppc

README.md

@@ -238,6 +238,7 @@ All solutions will be accepted!
 |654|[Maximum Binary Tree](https://leetcode-cn.com/problems/maximum-binary-tree/description/)|[java/py/js](./algorithms/MaximumBinaryTree)|Medium|
 |208|[Implement Trie Prefix Tree](https://leetcode-cn.com/problems/implement-trie-prefix-tree/description/)|[java/py/js](./algorithms/ImplementTriePrefixTree)|Medium|
 |114|[Flatten Binary Tree To Linked List](https://leetcode-cn.com/problems/flatten-binary-tree-to-linked-list/description/)|[java/py/js](./algorithms/FlattenBinaryTreeToLinkedList)|Medium|
+|284|[Peeking Iterator](https://leetcode-cn.com/problems/peeking-iterator/description/)|[java/py](./algorithms/PeekingIterator)|Medium|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/PeekingIterator/README.md

@@ -0,0 +1,2 @@
+# Peeking Iterator
+This problem is easy to solve

algorithms/PeekingIterator/Solution.java

@@ -0,0 +1,30 @@
+// Java Iterator interface reference:
+// https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
+class PeekingIterator implements Iterator<Integer> {
+    private Iterator<Integer> iterator;
+    private Integer top;
+    public PeekingIterator(Iterator<Integer> iterator) {
+        // initialize any member here.
+        this.iterator = iterator;
+        top = iterator.hasNext() ? iterator.next() : null;
+    }
+
+    // Returns the next element in the iteration without advancing the iterator.
+    public Integer peek() {
+        return top;
+    }
+
+    // hasNext() and next() should behave the same as in the Iterator interface.
+    // Override them if needed.
+    @Override
+    public Integer next() {
+        Integer temp = top;
+        top = iterator.hasNext() ? iterator.next() : null;
+        return temp;
+    }
+
+    @Override
+    public boolean hasNext() {
+        return top != null;
+    }
+}

algorithms/PeekingIterator/solution.py

@@ -0,0 +1,56 @@
+# Below is the interface for Iterator, which is already defined for you.
+#
+# 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
+#         """
+
+class PeekingIterator(object):
+    def __init__(self, iterator):
+        """
+        Initialize your data structure here.
+        :type iterator: Iterator
+        """
+        self.iterator = iterator
+        self.top = iterator.next() if iterator.hasNext() else None
+
+    def peek(self):
+        """
+        Returns the next element in the iteration without advancing the iterator.
+        :rtype: int
+        """
+        return self.top
+
+    def next(self):
+        """
+        :rtype: int
+        """
+        top = self.top
+        self.top = self.iterator.next() if self.iterator.hasNext() else None
+        return top
+
+    def hasNext(self):
+        """
+        :rtype: bool
+        """
+        return self.top != None
+
+# 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].