Initial data commit

Task/Permutations/Nim/permutations-2.nim

@@ -0,0 +1,23 @@
+iterator inplacePermutations[T](xs: var seq[T]): var seq[T] =
+    assert xs.len <= 24, "permutation of array longer than 24 is not supported"
+
+    let n = xs.len - 1
+    var
+      c: array[24, int8]
+      i: int = 0
+
+    for i in 0 .. n: c[i] = int8(i+1)
+
+    while true:
+      yield xs
+      if i >= n: break
+
+      c[i] -= 1
+      let j = if (i and 1) == 1: 0 else: int(c[i])
+      swap(xs[i+1], xs[j])
+
+      i = 0
+      while c[i] == 0:
+        let t = i+1
+        c[i] = int8(t)
+        i = t