How to build tree

#1

If i dont want to build a tree without -1 what should i do

#2

without -1 means??
what is your doubt??

#3

if while giving input i dont give -1 for null node what would be the code to build tree

#4

there should be something which tell us that now this is tree’s last point
otherwise we can’t build tree

#5

we can also build tree if any two traversals are given
preorder ,inorder, postorder