Swift Functional Programming - Second Edition

The contains method

Additionally, our contains method requires to be modified as it will search only in leaves. Let's improve this, assuming that our Tree is a BST:

static func contains(_ item: Element, tree: BST<Element>) -> Bool {     switch tree {     case .leaf:         return false     case .node(let lhs, let element, let rhs):         if item < element {             return contains(item, tree: lhs)         } else if item > element {             return contains(item, tree: rhs)         }         return true     } } 

This method searches for a specific element and returns true if it finds it in node.

The following presents an example usage of this method:

let isFound = BST.contains(9, tree: functionalBST) 

The isFound variable is going to be true in this case.