Spaces Apart

Create a function that takes an lst and returns the sum of the numbers between two "1"s.

Examples

space_apart([1, 0, 1, "1", 4, 3, 2, 3, 2, "1"]) ➞ 14

space_apart(["1", 9, 20, 38, "1"]) ➞ 67

space_apart([3, 2, 9, "1", 0, 0, -1, "1"]) ➞ "invalid"

Notes

• Return "invalid" if:
  • A negative number exists inside lst.
  • The number of "1"s does not equal 2.
• Ignore any other string inside lst.
• Note that "1" is not 1.