LeetCode/kt/construct-binary-tree-from-preorder-and-postorder-traversal.kt

class Solution {
    private data class Reconstruct(val preorder: IntArray, val postorder: IntArray) {
        private var pre: Int = 0
        private var post: Int = 0

        fun construct(): TreeNode? {
            val node = TreeNode(preorder[pre])
            ++pre

            if (node.`val` != postorder[post]) {
                node.left = construct()
            }

            if (node.`val` != postorder[post]) {
                node.right = construct()
            }

            ++post
            return node
        }
    }

    fun constructFromPrePost(
        preorder: IntArray,
        postorder: IntArray,
    ): TreeNode? = Reconstruct(preorder, postorder).construct()
}