o(15)g <-> t(20)

o(15)g-->""   o died, became 0
t(20)-->g(7)  t reduce to 1/3

o(15)g <-> t(20)

o(15)g-->"" t(20)-->g(7)

I am confused. Why the output of (t(20) - o(15)) is g(7) instead of e(5)_

Well, fixed. change next integer to closest integer.
Thanks for your feedback ;-)

My English is very poor ;-)
This sentence has modified for three times, if rounded up to the next integer is not means "use Math.round", I'm going to make the 4th changes. ;-)

 "dog"       <->   "cat"

d(4)og     <->  c(3)at
d(4)-->a(1)     c(3) -->""

a(1)og     <->  a(1)t
a(1)-->""       a(1)-->""

o(15)g     <->  t(20)
o(15)g-->""     t(20)-->g(7)

g(7)       <->  g(7)
g(7)-->""       g(7)-->""

Draw ;-)

At the first step, you calculate d(4)-->b(2) is wrong, 4/3=1.3333... Math.round(4/3)= 1 instead of 2

Fixed this. Thanks!