Movie Theater Seating

A group of n friends are going to see a movie. They would like to find a spot where they can sit next to each other in the same row. A movie theater's seat layout can be represented as a 2-D matrix, where 0s represent empty seats and 1s represent taken seats.

[[1, 0, 0, 0, 1, 1, 1],
[1, 1, 1, 0, 1, 1, 1],
[1, 0, 1, 0, 1, 0, 1],
[1, 1, 0, 1, 1, 0, 1],
[1, 0, 1, 1, 1, 1, 1],
[1, 0, 1, 1, 0, 0, 0]]

Create a function that, given a seat layout and the number of friends n, returns the number of available spots for all n friends to sit together. In the above example, if n = 3, there would be 2 spots (the first row and last row).

Examples

group_seats([
  [1, 0, 1, 0, 1, 0, 1],
  [0, 1, 0, 1, 0, 1, 0],
  [0, 0, 1, 1, 1, 1, 1],
  [1, 0, 1, 1, 0, 0, 1],
  [1, 1, 1, 0, 1, 0, 1],
  [0, 1, 1, 1, 1, 0, 0]
], 2) ➞ 3

group_seats([
  [1, 0, 1, 0, 1, 0, 1],
  [0, 1, 0, 0, 0, 0, 0],
], 4) ➞ 2

Notes

Multiple free arrangements that overlap still count as distinct arrangements (see example #2).