Given a binary tree, print out the tree in "plough" order. This is left to right, right to left, alternating on every row.

For example

      1
     2  3 

Should result in 1, 3, 2

A slightly more complicated example

      1
     2  3
    4 5 6 7
   8      9      
  10 11

Should give 1, 3, 2, 4, 5, 6, 7, 9, 8, 10, 11

https://projecteuler.net/problem=25

https://projecteuler.net/problem=7

https://projecteuler.net/problem=50

https://projecteuler.net/problem=11

https://projecteuler.net/problem=18

https://projecteuler.net/problem=67

https://projecteuler.net/problem=31

https://projecteuler.net/problem=15

https://projecteuler.net/problem=58