func levelOrder(_ root: TreeNode?) -> [[Int]] {
var queue: [TreeNode] = []
var toBePrint = 0
var nextLevelCount = 0
var result: [[Int]] = []
var temp: [Int] = []
if let r = root {
queue.append(r)
toBePrint += 1
}
while queue.isEmpty == false {
if let first = queue.first {
temp.append(first.val)
queue.removeFirst()
toBePrint -= 1
if let left = first.left {
queue.append(left)
nextLevelCount += 1
}
if let right = first.right {
queue.append(right)
nextLevelCount += 1
}
if toBePrint == 0 {
result.append(temp)
temp = []
toBePrint = nextLevelCount
nextLevelCount = 0
}
}
}
if temp.isEmpty == false {
result.append(temp)
}
return result
}