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/**

* Implement an iterator to flatten a 2d vector.

*

* Example:

*

* Input: 2d vector =

* [

* [1,2],

* [3],

* [4,5,6]

* ]

* Output: [1,2,3,4,5,6]

* Explanation: By calling next repeatedly until hasNext returns false,

* the order of elements returned by next should be: [1,2,3,4,5,6].

*

* Follow up:

* As an added challenge, try to code it using only iterators in C++ or

* iterators in Java.

*/

public class Flatten2DVector251 {

class Vector2D implements Iterator<Integer> {

private Iterator<List<Integer>> iter2d;

private Iterator<Integer> iter;

public Vector2D(List<List<Integer>> vec2d) {

iter2d = vec2d.iterator();

if (iter2d.hasNext()) {

iter = iter2d.next().iterator();

} else {

iter = (new ArrayList<Integer>()).iterator();

}

}

@Override

public Integer next() {

hasNext();

return iter.next();

}

@Override

public boolean hasNext() {

while (!iter.hasNext()) {

if (!iter2d.hasNext()) return false;

iter = iter2d.next().iterator();

}

return iter.hasNext();

}

}

/**

* Your Vector2D object will be instantiated and called as such:

* Vector2D i = new Vector2D(vec2d);

* while (i.hasNext()) v[f()] = i.next();

*/

}