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Problem solution · Turing

CCC 2005 J4 - Cross Spiral

CCC 2005 J4 - Cross Spiral: a Turing solution using direct simulation. Learn the idea, check the complexity, and read the full code, with credit to CCCSolutions.

Technique
Direct simulation
Source
CCCSolutions
Length
121 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Direct simulation

For CCC 2005 J4 - Cross Spiral, the implementation follows the problem’s operations directly while maintaining only the state needed for the next decision.

  1. Translate each rule into one explicit state update.
  2. Maintain the invariant after every processed item.
  3. Return the accumulated state once all relevant input has been handled.

Code notes

  • 121 lines of Turing from the credited upstream file ccc05j4.t.
  • The implementation keeps its working state in language-native values and containers.
  • No explicit loop blocks detected.

Complexity

Count the number and nesting of passes over the input, then include the maintained containers in the memory estimate.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from CCCSolutions by CCCSolutions contributors · Milliken Mills High School and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeCCC 2005 J4 - Cross Spiral · TuringTuring
Use this to learn the idea, then write your own version.
% CCC 2005 Junior problem 4% Cross Spiral%% a 2D array problem, with orientation paramount in a spiral% cross shape. Not too ugly, but...%% make the grid larger than necessary to give borders,% so bounds checking is not needed var g : array 0 .. 21, 0 .. 21 of booleanvar w, h, cw, ch : intvar c, r, direction : intvar steps : intvar moving : boolean get w, h, cw, ch, steps% initialize gridfor i : 0 .. 21    for j : 0 .. 21        if i >= 1 and i <= h and j >= 1 and j <= w and                not ( (i <= ch and (j <= cw or j > w - cw)) or                (i > h - ch and (j <= cw or j > w - cw))) then            g (i, j) := true        else            g (i, j) := false        end if    end forend for %- testing%- for i : 0 .. 21%-     for j : 0 .. 21%-         if g (i, j) then%-             put " " ..%-         else%-             put "*" ..%-         end if%-     end for%-     put ""%- end for%- var k : string (1)%- getch (k) c := cw + 1r := 1direction := 0for i : 1 .. steps    g (r, c) := false    moving := true    if direction = 0 then        if g (r - 1, c) then            r := r - 1            direction := 90        elsif g (r, c + 1) then            c := c + 1            direction := 0        elsif g (r + 1, c) then            r := r + 1            direction := 270        elsif g (r, c - 1) then            c := c - 1            direction := 180        else            moving := false        end if    elsif direction = 90 then        if g (r, c - 1) then            c := c - 1            direction := 180        elsif g (r - 1, c) then            r := r - 1            direction := 90        elsif g (r, c + 1) then            c := c + 1            direction := 0        elsif g (r + 1, c) then            r := r + 1            direction := 270        else            moving := false        end if    elsif direction = 180 then        if g (r + 1, c) then            r := r + 1            direction := 270        elsif g (r, c - 1) then            c := c - 1            direction := 180        elsif g (r - 1, c) then            r := r - 1            direction := 90        elsif g (r, c + 1) then            c := c + 1            direction := 0        else            moving := false        end if    elsif direction = 270 then        if g (r, c + 1) then            c := c + 1            direction := 0        elsif g (r + 1, c) then            r := r + 1            direction := 270        elsif g (r, c - 1) then            c := c - 1            direction := 180        elsif g (r - 1, c) then            r := r - 1            direction := 90        else            moving := false        end if    end if    exit when not moving end forput cput r

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