BinaryTreePostorderTraversal145.kt

package easy

/**
 * Given the root of a binary tree, return the postorder traversal of its nodes' values.



Example 1:


Input: root = [1,null,2,3]
Output: [3,2,1]
Example 2:

Input: root = []
Output: []
Example 3:

Input: root = [1]
Output: [1]


Constraints:

The number of the nodes in the tree is in the range [0, 100].
-100 <= Node.val <= 100


Follow up: Recursive solution is trivial, could you do it iteratively?
 */

val Result = mutableListOf<Int>()

fun postorderTraversal(root: TreeNode?): List<Int> {
    if(root == null)
        return Result

    postorderTraversal(root.left)
    postorderTraversal(root.right)
    Result.add(root.`val`)
    return list

}