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BinaryTreeLevelOrderTraversal.scala
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BinaryTreeLevelOrderTraversal.scala
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package BinaryTreeLevelOrderTraversal
/**
* Created by iodone on {19-10-18}.
*/
/**
* 解题报告
*
* 思路一:采用队列的方式,从root节点开始遍历,左右节点入队列,后续每次从队头取值然后左右子节点入队列,直到队列为空为止
*
* 思路二:递归思路,分解成root :: level(左子树)和level(右子树) zip即可
*/
class TreeNode(var _value: Int) {
var value: Int = _value
var left: TreeNode = null
var right: TreeNode = null
}
object Solution {
def levelOrder(root: TreeNode): List[List[Int]] = {
if (root == null) List()
else {
var leftQ = List(List(root))
var levelOrderList: List[List[Int]] = List()
while (leftQ.nonEmpty && leftQ.head != List()) {
levelOrderList = levelOrderList ::: leftQ.head.map(_.value) :: Nil
leftQ = leftQ.tail ::: leftQ.head.flatMap { n =>
List(n.left, n.right).filter(_ != null)
} :: Nil
}
levelOrderList
}
}
def levelOrder2(root: TreeNode): List[List[Int]] = {
if (root == null) List()
else {
List(root.value) :: levelOrder2(root.left).zipAll(levelOrder2(root.right), List(), List()).map(f => f._1 ::: f._2)
}
}
def main(args: Array[String]): Unit = {
val node0 = new TreeNode(5)
val node1 = new TreeNode(4)
val node2 = new TreeNode(7)
node0.left = node1
node0.right = node2
println(levelOrder2(node0))
}
}