BM24 二叉树的中序遍历

https://www.nowcoder.com/practice/0bf071c135e64ee2a027783b80bf781d

func inorderTraversal( root *TreeNode ) []int {
    result := make([]int, 0)
    inorder(root, &result)
    return result
}

func inorder(root *TreeNode, arr *[]int) {
    if root == nil {
        return
    }
    
    inorder(root.Left, arr)
    *arr = append(*arr, root.Val)
    inorder(root.Right, arr)
}