203 字
1 分钟
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：https://leetcode-cn.com/problems/binary-tree-level-order-traversal/
来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/cong-shang-dao-xia-da-yin-er-cha-shu-ii-lcof
题解
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}