[metapost] Drawing a urn

[Troy Henderson]

I was posting my solution as Dan replied.  Here's what I did.

Troy

   u:=5mm;
   s:=0.5*u;

   N:=57; % Number of "light" balls out of 100
   N:=max(min(N,100),0); % Make sure 0<=N<=100

   boolean b,b[];
   for n=1 upto N: b[n]:=true; endfor;
   for n=N+1 upto 100: b[n]:=false; endfor;

   path c;
   for n=100 downto 1:
      i:=floor((n-1)/10)+1;
      j:=n-10*(i-1);
      m:=floor(uniformdeviate (n-1))+1;
      b:=b[m]; b[m]:=b[n]; b[n]:=b; % Interchange b[m] and b[n]
      c:=fullcircle scaled u shifted (j*u-u/2+s,i*u-u/2+s);
      fill c withcolor if b: 0.7*white else: 0.4*white fi;
   endfor;

   draw (0,10u+s)--(0,.5u)..(.15u,.15u)..(.5u,0)
      --(9.5u+2s,0)..(9.85u+2s,.15u)..(10u+2s,.5u)--(10u+2s , 10u+s);