Add tasks for all the new languages

Task/Knights-tour/Sidef/knights-tour.sidef

@@ -0,0 +1,61 @@
+var board = []
+var I = 8
+var J = 8
+var F = (I*J > 99 ? '%3d' : '%2d')
+
+var (i, j) = (I.irand, J.irand)
+
+func from_algebraic(square) {
+     if (var match = square.match(/^([a-z])([0-9])\z/)) {
+         return(I - Num(match[1]), match[0].ord - 'a'.ord)
+     }
+     die "Invalid block square: #{square}"
+}
+
+func possible_moves(i,j) {
+    gather {
+        for ni,nj in [
+            [i-2,j-1], [i-2,j+1], [i-1,j-2], [i-1,j+2],
+            [i+1,j-2], [i+1,j+2], [i+2,j-1], [i+2,j+1],
+        ] {
+            if ((ni ~~ ^I) && (nj ~~ ^J) && !board[ni][nj]) {
+                take([ni, nj])
+            }
+        }
+    }
+}
+
+func to_algebraic(i,j) {
+    ('a'.ord + j).chr + Str(I - i)
+}
+
+if (ARGV[0]) {
+    (i, j) = from_algebraic(ARGV[0])
+}
+
+var moves = []
+for move in (1 .. I*J) {
+    moves << to_algebraic(i, j)
+    board[i][j] = move
+    var min = [9]
+    for target in possible_moves(i, j) {
+        var (ni, nj) = target...
+        var nxt = possible_moves(ni, nj).len
+        if (nxt < min[0]) {
+            min = [nxt, ni, nj]
+        }
+    }
+
+    (i, j) = min[1,2]
+}
+
+say (moves/4 -> map { .join(', ') }.join("\n") + "\n")
+
+for i in ^I {
+    for j in ^J {
+        (i%2 == j%2) && print "\e[7m"
+        F.printf(board[i][j])
+        print "\e[0m"
+    }
+    print "\n"
+}