Binary Tree Level Order Traversal leetcode https://leetcode.com/problems/binary-tree-level-order-traversal/ Swift solution

BinaryTreeLevelOrderTraversal.swift

func levelOrderTraversal(root:TreeNode) -> [[Int]]{
    var outerArr = [[Int]]()
    var levelNode = [TreeNode]()
    var nextLevelNode = [TreeNode]()
    levelNode.append(root)
    var innerArr = [Int]()
    
    while !levelNode.isEmpty{
        let currentNode = levelNode.removeAtIndex(0)
        innerArr.append(currentNode.val)
        if let left = currentNode.left{
            nextLevelNode.append(left)
        }
        if let right = currentNode.right{
            nextLevelNode.append(right)
        }
        
        if levelNode.isEmpty{
            let arr = innerArr
            outerArr.append(arr)
            levelNode += nextLevelNode
            nextLevelNode.removeAll()
            innerArr.removeAll()
        }
        
    }
    
    return outerArr
}