[swift] LeetCode 114. Flatten Binary Tree to Linked List

Given a binary tree, flatten it to a linked list in-place.

For example, given the following tree:

/ \

2 5

/ \ \

3 4 6

The flattened tree should look like:

func flatten(_ root: TreeNode?) {
    if let p = root {
        flatten(p.left)
        flatten(p.right)
        if let l = p.left {
            if let r = p.right {
                var lr = l
                while lr.right != nil {
                    lr = lr.right!
                }
                lr.right = r
            }
            p.right = l
            p.left = nil
        }
    }
}

func flatten(_ root: TreeNode?) {

if let p = root {

flatten(p.left)

flatten(p.right)

if let l = p.left {

if let r = p.right {

var lr = l

while lr.right != nil {

lr = lr.right!

}

lr.right = r

}

p.right = l

p.left = nil

}