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# 32.II.从上到下打印二叉树II
## 题目
从上到下按层打印二叉树，同一层的节点按从左到右的顺序打印，每一层打印到一行。
例如:
给定二叉树: \[3,9,20,null,null,15,7],
```
3
/ \
9 20
/ \
15 7
```
返回其层次遍历结果：
```
[
[3],
[9,20],
[15,7]
]
```
提示：
节点总数 <= 1000
注意：本题与主站 102 题相同：
来源：力扣（LeetCode）
链接：
## 题解
```swift
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
}
```
