1+ #include < iostream>
2+ #include < queue>
3+ #include < vector>
4+ #include < assert.h>
5+ #include < algorithm>
6+ using namespace std ;
7+ 8+ class Iterator {
9+ const vector<int >* nums;
10+ int index;
11+ public:
12+ Iterator (const vector<int >& nums) {
13+ this ->nums = &nums;
14+ this ->index = 0 ;
15+ }
16+ Iterator (const Iterator& iter);
17+ 18+ // Returns the next element in the iteration.
19+ int next () {
20+ return (*nums)[index++];
21+ }
22+ 23+ // Returns true if the iteration has more elements.
24+ bool hasNext () const {
25+ return index < (*nums).size ();
26+ }
27+ };
28+ 29+ class PeekingIterator : public Iterator {
30+ private:
31+ int nextElement;
32+ bool flag;
33+ public:
34+ PeekingIterator (const vector<int >& nums) : Iterator(nums) {
35+ // Initialize any member here.
36+ // **DO NOT** save a copy of nums and manipulate it directly.
37+ // You should only use the Iterator interface methods.
38+ flag = Iterator::hasNext ();
39+ if (flag) {
40+ nextElement = Iterator::next ();
41+ }
42+ }
43+ 44+ // Returns the next element in the iteration without advancing the iterator.
45+ int peek () {
46+ return nextElement;
47+ }
48+ 49+ // hasNext() and next() should behave the same as in the Iterator interface.
50+ // Override them if needed.
51+ int next () {
52+ int ret = nextElement;
53+ flag = Iterator::hasNext ();
54+ if (flag) {
55+ nextElement = Iterator::next ();
56+ }
57+ return ret;
58+ }
59+ 60+ bool hasNext () const {
61+ return flag;
62+ }
63+ };
64+ 65+ // Test
66+ int main ()
67+ {
68+ /* * 用gcc/g++编译, 需要用这种方式初始化vector:
69+ */
70+ int a[3 ] = {1 , 2 , 3 };
71+ vector<int > nums (a, a + 3 );
72+ 73+ PeekingIterator peekingIterator (nums);
74+ assert (1 == peekingIterator.next ());
75+ assert (2 == peekingIterator.peek ());
76+ assert (2 == peekingIterator.next ());
77+ assert (3 == peekingIterator.next ());
78+ assert (!peekingIterator.hasNext ());
79+ 80+ cout << " OK~"
81+ 82+ return 0 ;
83+ }
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