[LeetCode 251] Flatten 2D Vector

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].

Hint:

• 1. How many variables do you need to keep track?
• 1. Two variables is all you need. Try with x and y.
• 1. Beware of empty rows. It could be the first few rows.
• 1. To write correct code, think about the invariant to maintain. What is it?
• 1. The invariant is x and y must always point to a valid point in the 2d vector. Should you maintain your invariant ahead of time or right when you need it?
• 1. Not sure? Think about how you would implement hasNext(). Which is more complex?
• 1. Common logic in two different places should be refactored into a common method.

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

Diffculty
Medium

Similar Problems

Analysis

http://www.cnblogs.com/grandyang/p/5209621.html