March 2014 update

Task/Combinations/Haskell/combinations-7.hs

@@ -0,0 +1,5 @@
+comb :: Int -> [a] -> [[a]]
+comb m xs = combsBySize xs !! m
+ where
+   combsBySize = foldr f ([[]] : repeat [])
+   f x next = zipWith (++) (map (map (x:)) ([]:next)) next

Task/Combinations/OCaml/combinations-2.ocaml

@@ -0,0 +1,16 @@
+let comb m xs =
+  let xs = Array.of_list xs in
+  if m > Array.length xs then
+    []
+  else begin
+    let arr = Array.make (m+1) [] in
+    arr.(0) <- [[]];
+    for j = 0 to Array.length xs - m do
+      for i = 1 to m do
+        arr.(i) <- arr.(i) @ List.map (fun ys -> xs.(j+i-1)::ys) arr.(i-1)
+      done
+    done;
+    arr.(m)
+  end
+;;
+comb 3 [0;1;2;3;4];;

Task/Combinations/Perl-6/combinations-1.pl6

@@ -1 +1 @@
-.say for (^5).list.combinations(3).tree;
+.say for combinations(5,3);

Task/Combinations/Rust/combinations.rust

@@ -0,0 +1,30 @@
+fn comb<T: std::fmt::Default>(arr: &[T], n: uint) {
+  let mut incl_arr: ~[bool] = std::vec::from_elem(arr.len(), false);
+  comb_intern(arr, n, incl_arr, 0);
+}
+
+fn comb_intern<T: std::fmt::Default>(arr: &[T], n: uint, incl_arr: &mut [bool], index: uint) {
+  if (arr.len() < n + index) { return; }
+  if (n == 0) {
+    let mut it = arr.iter().zip(incl_arr.iter()).filter_map(|(val, incl)|
+      if (*incl) { Some(val) } else { None }
+    );
+    for val in it { print!("{} ", *val); }
+    print("\n");
+    return;
+  }
+
+  incl_arr[index] = true;
+  comb_intern(arr, n-1, incl_arr, index+1);
+  incl_arr[index] = false;
+
+  comb_intern(arr, n, incl_arr, index+1);
+}
+
+fn main() {
+  let arr1 = ~[1, 2, 3, 4, 5];
+  comb(arr1, 3);
+
+  let arr2 = ~["A", "B", "C", "D", "E"];
+  comb(arr2, 3);
+}

Task/Combinations/TXR/combinations.txr

@@ -0,0 +1,5 @@
+@(do
+   (defun comb-n-m (n m)
+     (comb (range* 0 n) m))
+
+   (put-line `3 comb 5 = @(comb-n-m 5 3)`))