/* Computes the nth Fibonacci number several ways & compares their running times. */
fun main(args: Array<String>) {
    val n = 43
    test(n, "dpFib", ::dpFib)
    test(n, "memFib", ::memFib)
    test(n, "naiveFib", ::naiveFib)
}

/* Test harness. */
fun test(n: Int, fname: String, f: (Int) -> Int) {
    var result = 0
    val exeTime = kotlin.system.measureTimeMillis { result = f(n) }
    println("Running $fname($n) gives $result and it takes $exeTime ms to execute.")
}

/////////////////////////////////////////////////////////////////////////////
/* Computes the nth Fibonacci number using the recurrence naively. */
fun naiveFib(n: Int): Int = if (n < 2) n else naiveFib(n-1) + naiveFib(n-2)

/////////////////////////////////////////////////////////////////////////////
/* Computes the nth Fibonacci number using bottom-up dynamic programming. */
fun dpFib(n: Int): Int {
    val table = IntArray(n+1) { it }
    for (i in 2..n) table[i] = table[i-1] + table[i-2]
    return table[n]
}

/////////////////////////////////////////////////////////////////////////////
/* Computes the nth Fibonacci number using memoization. */
fun memFib(n: Int): Int {
    val UNKNOWN = -1
    val table = IntArray(n+1) { if (it < 2) it else UNKNOWN }
    fun accessTable(k: Int): Int {
        if (table[k] == UNKNOWN)
            table[k] = accessTable(k-1) + accessTable(k-2)
        return table[k]
    }
    return accessTable(n)
}