题解 | 求二叉树的层序遍历

/**
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */
import java.util.LinkedList
import java.util.Queue
import java.util.ArrayDeque
object Solution {
    /**
    * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
    *
    * 
        * @param root TreeNode类 
        * @return int整型二维数组
    */
    fun levelOrder(root: TreeNode?): Array<IntArray>  {
        // write code here
       if (root == null) return emptyArray()
       val list = mutableListOf<IntArray>()
       val queue = ArrayDeque<TreeNode>()
       queue.addLast(root)
       while(queue.isNotEmpty()){
        val levelSize = queue.size
        val curValues = mutableListOf<Int>()
        repeat(levelSize){
            val node = queue.removeFirst()
            curValues.add(node.`val`)
            node.left?.let{queue.addLast(it)}
            node.right?.let{queue.addLast(it)}
        }
        list.add(curValues.toIntArray())
       }
       return list.toTypedArray()
    }
}