Prefix infix suffix expression (written conversion)

Prefix infix suffix expression , In the final analysis, it is the traversal of the pre order, middle order and post order of the tree , So if you have learned the depth first traversal of trees , Such a transformation is small for you case 了 .

We know , If the infix expression is ：2 + 6, The prefix expression is ：+ 2 6, The postfix expression is 2 6 +. It can be concluded here that , When calculating expressions , No matter how to convert the form , The left and right numbers of binary operators will not change order , Only the position of the symbol is changed .

And then something magical happened

Expression and tree are perfectly combined ！

Then I don't need to say more ！

+ 2 6 Prefix expression It is also preorder traversal

2 + 6 Infix expression It is also a middle order traversal

2 6 + Postfix expression Post order traversal again

This is the wonderful use of trees , It's also X The essence of infix expression ！