LeetCode/swift/binary-tree-inorder-traversal.swift

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init() { self.val = 0; self.left = nil; self.right = nil; }
 *     public init(_ val: Int) { self.val = val; self.left = nil; self.right = nil; }
 *     public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
 *         self.val = val
 *         self.left = left
 *         self.right = right
 *     }
 * }
 */
class Solution {
    func inorderTraversal(_ root: TreeNode?, _ values: inout [Int]) {
        if let root = root {
            inorderTraversal(root.left, &values)
            values.append(root.val)
            inorderTraversal(root.right, &values)
        }
    }

    func inorderTraversal(_ root: TreeNode?) -> [Int] {
        var traversal: [Int] = []
        inorderTraversal(root, &traversal)
        return traversal
    }
}