Implement an iterator to flatten a 2d vector.
For example,
Given 2d vector =
[
[1,2],
[3],
[4,5,6]
]
By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,2,3,4,5,6].
Solution：Iterator
思路：
Time Complexity: O() Space Complexity: O()
Solution Code：
public class Vector2D implements Iterator<Integer> {
private Iterator<List<Integer>> i;
private Iterator<Integer> j;
public Vector2D(List<List<Integer>> vec2d) {
i = vec2d.iterator();
}
@Override
public Integer next() {
hasNext();
return j.next();
}
@Override
public boolean hasNext() {
while ((j == null || !j.hasNext()) && i.hasNext())
j = i.next().iterator();
return j != null && j.hasNext();
}
}
