### how to find predecessor in the tree

Posted:

**Sat Nov 22, 2014 1:43 pm**Hello, Could you help me with a function, I need to find the predecessor in the tree, but my function always returns an empty list,

- Code: Select all
`(define (predecessor element tree)`

(cond

((null? tree) (node tree) ) ; If the tree is null result is the needed element

((> element (node tree)) (mem element (right-branch tree))); if the element is greater than node element, we search it in the right-branch tree

((< element (node tr)) (mem element (left-branch tree))) ; if element is lesser than node element, we search it in the left-branch tree

)

)