284.peeking_iterator.md

Author: newdee

284.peeking_iterator.md

@@ -0,0 +1,76 @@
+[To Index](/index.md)
+---
+# 284.Peeking Iterator
+难度:Medium
+> 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?
+
+We can set a right value stands for next value, a bool stands for hasNext() function.  
+Codes are as follows:  
+
+```
+// 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;
+public:
+	Iterator(const vector<int>& nums);
+	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 {
+int right;
+bool flag;
+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.
+        flag= Iterator::hasNext();
+       right  = Iterator::next();
+	}
+
+    // Returns the next element in the iteration without advancing the iterator.
+	int peek() {      
+        return right;
+	}
+
+	// hasNext() and next() should behave the same as in the Iterator interface.
+	// Override them if needed.
+	int next() {
+        int cur=right;
+        flag = Iterator::hasNext();
+        if(flag) 
+        {
+           right  = Iterator::next();
+        }
+	    return cur;
+	}
+
+	bool hasNext() const {
+	    return flag;
+	}
+};
+```
+> 执行用时 :8 ms, 在所有 C++ 提交中击败了64.25%的用户   
+内存消耗 :9.9 MB, 在所有 C++ 提交中击败了38.30%的用户

SUMMARY.md

@@ -76,6 +76,7 @@ Leetcode Index
 - [263.Ugly Numbers](/263.ugly_numbers.md)
 - [268.Missing Number](/268.missing_number.md)
 - [278.First Bad Version](/278.first_bad_version.md)
+- [284.Peeking Iterator](/284.peeking_iterator.md)
 - [290.Word Pattern](/290.word_pattern.md)
 - [282.Nim Game](/292.nim_game.md)
 - [303.Range Sum Query Immutable](/303.range_sum_query_immutable.md)

index.md

@@ -76,6 +76,7 @@ Leetcode Index
 - [263.Ugly Numbers](/263.ugly_numbers.md)
 - [268.Missing Number](/268.missing_number.md)
 - [278.First Bad Version](/278.first_bad_version.md)
+- [284.Peeking Iterator](/284.peeking_iterator.md)
 - [290.Word Pattern](/290.word_pattern.md)
 - [282.Nim Game](/292.nim_game.md)
 - [303.Range Sum Query Immutable](/303.range_sum_query_immutable.md)