ACM International Collegiate Programming Contest, Asia Regional (Tokyo), 2007, Problem A

gistfile1.sml

fun remove_a_stone vec i =
    let
        open VectorSlice
        val size = Vector.length vec - 1
        val newvec = 
            if i = 0 then vector (slice (vec, 1, SOME size))
            else if i = size then vector (slice (vec, 0, SOME size))
            else concat [slice (vec, 0, SOME i),
                         slice (vec, i+1, SOME (size-i))]
    in
        (newvec, i mod size)
    end

fun solve_one n k m =
    let
        val vec = Vector.tabulate (n, fn i => i+1)
        fun remove_stones vec k m =
            if Vector.length vec = 1 then Vector.sub (vec, 0)
            else
                let
                    (* val stone = Vector.sub (vec, m) *)
                    val (newvec, newm) = remove_a_stone vec m
                    val size = Vector.length newvec
                in
                    (*
                     TextIO.output (TextIO.stdOut, Int.toString stone ^ " ");
                     *)
                    remove_stones newvec k ((newm + k - 1) mod size)
                end
    in
        remove_stones vec k (m - 1)
    end

fun solve file =
    let
        open TextIO
        val f = openIn file
        val line = ref NONE
        fun split s = String.tokens (fn c => c = #" ") s
        fun toIntList l = List.map (fn s => valOf (Int.fromString s)) l
    in
        while (line := inputLine f; !line <> SOME "0 0 0\n") do
            let
                val params = toIntList (split (valOf (!line)))
                val n = hd params
                val k = List.nth (params, 1)
                val m = List.nth (params, 2)
                val result = solve_one n k m
            in
                output (stdOut, Int.toString result ^ "\n")
            end;
        closeIn f
    end