binary-tree-level-order-traversal

binary-tree-level-order-traversal.swift

class Solution {
    
    func levelOrder(_ root: TreeNode?) -> [[Int]] {
        guard let root = root else { return [] }
     
        var q = [TreeNode]()
        var lists = [[Int]]()
        q.append(root)
     
        while !q.isEmpty {
            lists.append(q.map { $0.val })
            print(lists, "list")
            q = q.reduce([]) { l, t in
                l + [t.left, t.right] // [] + [2,2] = [2,2]
                }.compactMap({$0})
        }
        
        return lists
    }
    
}

var rootTest = TreeNode(3, TreeNode(9), TreeNode(20, TreeNode(15), TreeNode(7)))
var tlal = TreeNode(3, TreeNode(2, TreeNode(10), TreeNode(10)), TreeNode(2, TreeNode(10), TreeNode(10)))

Solution().levelOrder(tlal)