https://leetcode.com/problems/zigzag-iterator/description/
public class ZigzagIterator {
private Iterator<Integer> iter1, iter2;
private Iterator<Integer> nextIter;
public ZigzagIterator(List<Integer> v1, List<Integer> v2) {
iter1 = v1.iterator();
iter2 = v2.iterator();
// pay attention here. list1 could be empty
nextIter = iter1.hasNext() ? iter1 : iter2;
}
public int next() {
int nextInt = nextIter.next();
if (nextIter == iter1 && iter2.hasNext()) {
nextIter = iter2;
} else if (nextIter == iter2 && iter1.hasNext()) {
nextIter = iter1;
}
return nextInt;
}
public boolean hasNext() {
return nextIter.hasNext();
// return iter1.hasNext() || iter2.hasNext();
}
}
Follow up
Extend to multiple lists of integers.
public class ZigzagIterator {
private LinkedList<Iterator> iterators;
public ZigzagIterator(List<List<Integer>> lists) {
iterators = new LinkedList<Iterator>();
for (List<Integer> list: lists) {
if (list != null && !list.isEmpty()) {
iterators.add(list.iterator());
}
}
}
public int next() {
Iterator<Integer> iter = iterators.removeFirst();
int nextInt = iter.next();
if (iter.hasNext()) {
iterators.add(iter);
}
return nextInt;
}
public boolean hasNext() {
return !iterators.isEmpty();
}
}
Runtime: O(1)
Space: O(n) n is lists.size()
