251. Flatten 2D Vector

Design and implement an iterator to flatten a 2d vector. It should support the following operations: next
and hasNext.

Example:

Vector2D iterator = new Vector2D([[1,2],[3],[4]]);

iterator.next(); // return 1
iterator.next(); // return 2
iterator.next(); // return 3
iterator.hasNext(); // return true
iterator.hasNext(); // return true
iterator.next(); // return 4
iterator.hasNext(); // return false



Notes:

    Please remember to RESET your class variables declared in Vector2D, as static/class variables are
    persisted across multiple test cases. Please see here for more details.
    You may assume that next() call will always be valid, that is, there will be at least a next element in
    the 2d vector when next() is called.



Follow up:

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

class Vector2D {
    int i = 0, j = 0;
    int[][] nums;
    public Vector2D(int[][] v) {
        nums = v;
    }

    public int next() {
        hasNext();
        int v = nums[i][j];
        if(j == nums[i].length-1) {
            j = 0;
            i++;
        } else {
            j++;
        }
        return v;
    }

    public boolean hasNext() {
        while(i < nums.length && nums[i].length == 0) i++;
        if(i == nums.length) return false;
        return true;
    }
}