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2 | 2 | // https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
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3 | 3 |
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4 | 4 | class PeekingIterator implements Iterator<Integer> {
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5 |
| - Integer nextElement; |
6 |
| - Iterator<Integer> iterator; |
| 5 | + private Iterator<Integer> iterator; |
| 6 | + private Integer topElement; |
| 7 | + |
7 | 8 | public PeekingIterator(Iterator<Integer> iterator) {
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8 | 9 | // initialize any member here.
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9 | 10 | this.iterator = iterator;
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10 |
| - updateNext(); |
11 |
| - } |
12 |
| - |
13 |
| - private void updateNext() { |
14 |
| - nextElement = iterator.hasNext() ? iterator.next() : null; |
| 11 | + populateTopElement(); |
15 | 12 | }
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16 |
| - |
| 13 | + |
17 | 14 | // Returns the next element in the iteration without advancing the iterator.
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18 | 15 | public Integer peek() {
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19 |
| - return nextElement; |
| 16 | + return this.topElement; |
| 17 | + } |
| 18 | + |
| 19 | + // hasNext() and next() should behave the same as in the Iterator interface. |
| 20 | + // Override them if needed. |
| 21 | + @Override |
| 22 | + public Integer next() { |
| 23 | + Integer nextValue = this.topElement; |
| 24 | + populateTopElement(); |
| 25 | + return nextValue; |
| 26 | + } |
| 27 | + |
| 28 | + @Override |
| 29 | + public boolean hasNext() { |
| 30 | + return this.topElement != null; |
| 31 | + } |
| 32 | + |
| 33 | + private void populateTopElement() { |
| 34 | + this.topElement = this.iterator.hasNext() ? this.iterator.next() : null; |
20 | 35 | }
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21 |
| - |
22 |
| - // hasNext() and next() should behave the same as in the Iterator interface. |
23 |
| - // Override them if needed. |
24 |
| - @Override |
25 |
| - public Integer next() { |
26 |
| - Integer returnValue = nextElement; |
27 |
| - updateNext(); |
28 |
| - return returnValue; |
29 |
| - } |
30 |
| - |
31 |
| - @Override |
32 |
| - public boolean hasNext() { |
33 |
| - return nextElement != null; |
34 |
| - } |
35 | 36 | }
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