题解 | 二叉树的前序遍历

/**
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */
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整型一维数组
    */
    fun preorderTraversal(root: TreeNode?): IntArray  {
        // write code here
        val result = mutableListOf<Int>()
        dfsPreOrder(root,result)
        return result.toIntArray()
    }
    fun dfsPreOrder(root:TreeNode?,result:MutableList<Int>){
        if(root==null)return
        result.add(root.`val`)
        dfsPreOrder(root.left,result)
        dfsPreOrder(root.right,result)
    }
}