Solution URL
https://leetcode.com/submissions/detail/415269877/
代码
// Java Iterator interface reference:
// https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
import java.util.NoSuchElementException;
class PeekingIterator implements Iterator<Integer> {
private Iterator<Integer> it;
private Integer peekValue;
public PeekingIterator(Iterator<Integer> iterator) {
// initialize any member here.
it = iterator;
peekValue = null;
}
// Returns the next element in the iteration without advancing the iterator.
public Integer peek() {
//check whether it has next or not
if(peekValue == null){
//check is there a next value or not
while(!it.hasNext()){
throw new NoSuchElementException();
}
//it has next, so can invocate next function
peekValue = it.next();
}
return peekValue;
}
// hasNext() and next() should behave the same as in the Iterator interface.
// Override them if needed.
@Override
public Integer next() {
//check peekValue has value or not; if has, then that is the next value
//or invocate next function
if(peekValue != null){
int returnValue = peekValue;
peekValue = null;//it must be reset here!
return returnValue;
}
return it.next();
}
@Override
public boolean hasNext() {
return peekValue != null || it.hasNext();
}
}
