The function is given a map with 1 representing land, 0 representing water. A land cell can have four neighbors along its edges. Compute the total perimeter of shore-lines that are defined by land cells touching water or the outer edges of the map. Each cell edge has a length equal to 1. An isolated cell without neighbors has a total perimeter length of 4.

Examples

islands_perimeter([
  [0, 1, 0, 0],
  [1, 1, 1, 0],
  [0, 1, 0, 0],
  [1, 1, 0, 0]
]) ➞ 16

islands_perimeter([
  [1, 1, 1, 1, 1, 1],
  [1, 0, 0, 0, 0, 1],
  [1, 0, 1, 1, 0, 1],
  [1, 0, 0, 0, 0, 1],
  [1, 1, 1, 1, 1, 1],
]), 42)

islands_perimeter([
  [1, 0]
]) ➞ 4

Notes

N/A