题目
二叉树的层次遍历
给定一个二叉树，返回其按层次遍历的节点值。 （即逐层地，从左到右访问所有节点）。
示例:
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]
]
代码：
/**
* Definition for a binary tree node.
* public class TreeNode {
* public var val: Int
* public var left: TreeNode?
* public var right: TreeNode?
* public init(_ val: Int) {
* self.val = val
* self.left = nil
* self.right = nil
* }
* }
*/
class Solution {
func levelOrder(_ root: TreeNode?) -> [[Int]] {
var intList:[[Int]] = [[Int]]()
var nodeList:[TreeNode] = [TreeNode]()
guard let root = root else {
return intList
}
nodeList.append(root)
while nodeList.isEmpty == false {
var count = nodeList.count
var temp = [Int]()
while count != 0 {
let node = nodeList.removeFirst()
temp.append(node.val)
if node.left != nil {
nodeList.append(node.left!)
}
if node.right != nil {
nodeList.append(node.right!)
}
count = count - 1
}
intList.append(temp)
}
return intList
}
}
