Diagonal Snake from a Rectangular Matrix

The function is given a rectangular list of lists of numbers. Make a list from these numbers in the order of connecting diagonals like a snake before the strike. Starting from the left-up corner:

• First diagonal, going up: [0][0]
• Second diagonal, going down: [0][1] -> [1][0]
• Third diagonal, going up: [2][0] -> [1][1] -> [0][2]
• etc, alternate between going up and going down
• Last diagonal: [rows - 1][cols -1]

Examples

diagonal_snake([
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
]) ➞ [1, 2, 4, 7, 5, 3, 6, 8, 9]

diagonal_snake([[3], [2]]) ➞ [3, 2]

diagonal_snake([[9]]) ➞ [9]

diagonal_snake([]) ➞ []

diagonal_snake([[9, 8, 7]]) ➞ [9, 8, 7]

Notes

N/A