Data update

Task/Van-Eck-sequence/Agena/van-eck-sequence.agena

@@ -0,0 +1,26 @@
+scope # find elements of the Van Eck Sequence - first term is 0, following
+      # terms are 0 if the previous was the first appearance of the element
+      #        or how far back in the sequence the last element appeared otherwise
+
+    local procedure VanEck( n :: number ) :: sequence # returns the first n elements of the Van Eck sequence
+        local constant result := seq(); for i to n do result[ i ] := 0 od;
+        local constant pos    := seq(); for i to n + 1 do pos[ i ] := 0 od;
+        for i from 2 to n do
+            local constant j    := i - 1;
+            local constant prev := result[ j ] + 1; # prev is indexed from 1, not 0
+            if pos[ prev ] <> 0 then
+                # not a new element
+                result[ i ] := j - pos[ prev ]
+            fi;
+            pos[ prev ] := j
+        od;
+        return result
+    end;
+
+    local constant veSeq := VanEck( 1000 ); # construct the first 1000 terms of the sequence
+    # show the first and last 10 elements
+    for i to 10 do printf( " %d", veSeq[ i ] ) od;
+    printf( "\n" );
+    for i from size veSeq - 9 to size veSeq do printf( " %d", veSeq[ i ] ) od;
+    printf( "\n" )
+end

Task/Van-Eck-sequence/Pluto/van-eck-sequence.pluto

@@ -0,0 +1,26 @@
+do  --[[ find elements of the Van Eck Sequence - first term is 0, following
+         terms are 0 if the previous was the first appearance of the element
+            or how far back in the sequence the last element appeared otherwise
+      ]]
+    local fmt = require( "fmt" )                          -- RC formatting module
+
+    local function VanEck( n : number ) : table -- returns the first n elements of the Van Eck sequence
+        local result <const> = {}     for i = 1, n     do result[ i ] = 0 end
+        local pos    <const> = {}     for i = 1, n + 1 do pos[    i ] = 0 end
+        for i = 2, n do
+            local j    <const> = i - 1
+            local prev <const> = result[ j ] + 1; -- prev is indexed from 1, not 0
+            if pos[ prev ] != 0 then
+                -- not a new element
+                result[ i ] = j - pos[ prev ]
+            end
+            pos[ prev ] = j
+        end
+        return result
+    end
+
+    local veSeq <const> = VanEck( 1000 )  -- construct the first 1000 terms of the sequence
+    -- show the first and last 10 elements
+    fmt.lprint( veSeq:slice( 1, 10 ) )
+    fmt.lprint( veSeq:slice( # veSeq - 9, # veSeq ) )
+end