251 - Flatten 2D Vector

Details

Key	Value
Link	https://leetcode.com/problems/flatten-2d-vector/
Language	Python 3
Runtime	146 ms, faster than 28.49% of Python3 online submissions for Flatten 2D Vector
Memory Usage	19.3 MB, less than 52.37% of Python3 online submissions for Flatten 2D Vector
Datastructures	List[List[int]]
Algorithms	Flatten in Constructor
Complexity	Time: O(N+V) Memory: O(N) (N=number of ints in vector, V=number of inner vectors)

Notes

Here's a Stackoverflow discussion that's helpful for understanding generators:

Generators are a simple and powerful tool for creating iterators. They are written like regular functions but use the yield statement whenever they want to return data. Each time next() is called on it, the generator resumes where it left off (it remembers all the data values and which statement was last executed).

Also note that a two-pointer solution would be more space efficient.

Procedure

1. ...

Code

class Vector2D:

    def __init__(self, vec: List[List[int]]):
        #def generator():
        #    for row in vec:
        #        for col in row: yield col
        #self.gen = generator()
        self.gen = (col for row in vec for col in row)
        self.next_val = next(self.gen, None)

    def next(self) -> int:
        result = self.next_val
        self.next_val = next(self.gen, None)
        return result

    def hasNext(self) -> bool:
        return self.next_val is not None    

# Your Vector2D object will be instantiated and called as such:
# obj = Vector2D(vec)
# param_1 = obj.next()
# param_2 = obj.hasNext()