get post order of binary tree from it's pre order and inner order

getPostOrder.kt

fun main() {
    testGetPostOrder()
}

fun testGetPostOrder() {
    val testSet = arrayOf(
            Triple(arrayOf(7, 5, 1, 6, 2, 9, 4, 3, 8), arrayOf(1, 5, 2, 6, 9, 7, 3, 4, 8), arrayOf(1, 2, 9, 6, 5, 3, 8, 4, 7)),
            Triple(arrayOf(1, 2, 3), arrayOf(2, 1, 3), arrayOf(2, 3, 1)),
            Triple(arrayOf(2, 3, 1), arrayOf(1, 2, 3), null),
            Triple(arrayOf(9, 6, 7, 2, 3, 4, 5, 8), arrayOf(7, 6, 3, 2, 4, 9, 8, 5), arrayOf(7, 3, 4, 2, 6, 8, 5, 9))
    )

    testSet.forEach {
        println("-case-")
        println("expected: ${it.third?.joinToString(separator = ", ")}")
        val result = getPostOrder(it.first, it.second)
        println("actually: ${result?.joinToString(separator = ", ")}")
        println("ok? ${it.third.contentEquals(result)}")
        println()
    }
}

fun getPostOrder(preOrder: Array<Int>, innerOrder: Array<Int>): Array<Int>? {
    var result = Array<Int>(0) {0}
    val headPos = innerOrder.indexOf(preOrder[0])
    val rightStart = headPos+1;
    val end = preOrder.size;

    for (i in 0 until headPos) {
        for (j in i+1 until end) {
            if (preOrder[j] == innerOrder[i]) {
                result = result.plus(innerOrder[i])
            }
        }
    }

    for (i in headPos-1 downTo 0) {
        if (preOrder[i] == innerOrder[i]) {
            result = result.plus(innerOrder[i])
        }
    }

    for (i in 0 until headPos) {
        for (j in i-1 downTo 1) {
            if (preOrder[j] == innerOrder[i]) {
                result = result.plus(innerOrder[i])
            }
        }
    }

    for (i in rightStart until end) {
        for (j in i+1 until end) {
            if (preOrder[j] == innerOrder[i]) {
                result = result.plus(innerOrder[i])
            }
        }
    }

    for (i in headPos until end) {
        if (preOrder[i] == innerOrder[i]) {
            result = result.plus(innerOrder[i])
        }
    }

    for (i in rightStart until end) {
        for (j in i-1 downTo headPos+1) {
            if (preOrder[j] == innerOrder[i]) {
                result = result.plus(innerOrder[i])
            }
        }
    }

    result = result.plus(preOrder[0])

    if (result.size == end) {
        return result
    }
    return null
}