function W = solver(B)

function path = simplepath(row,col,label)
% fprintf('simple path, r=%d c=%d, r=%d c=%d\n', row(1), col(1), row(2), col(2));
deltar = row(1) - row(2);
deltac = col(1) - col(2);
dr = sign(deltar);
dc = sign(deltac);


% adjacent
if (abs(deltar) == 1 && dc == 0) || (dr == 0 && abs(deltac) == 1)
    path = [row(1) col(1) row(2) col(2)];
    return
end

% try step to next row
if dr ~= 0
    r = row(2) + dr;
    c = col(2);
    if B(r,c) == label
        path = [r c row(2) col(2)];
%         fprintf('found a wire %d\n', label);
        return
    end
    if B(r,c) == 0
        path = simplepath([row(1) r], [col(1) c], label);
        if size(path,1) > 0
            path = [path; r c row(2) col(2)];
            return
        end
    end
end

% try step to next col
if dc ~= 0
    r = row(2);
    c = col(2) + dc;
    if B(r,c) == label
        path = [r c row(2) col(2)];
%         fprintf('found a wire %d\n', label);
        return
    end
    if B(r,c) == 0
        path = simplepath([row(1) r], [col(1) c], label);
        if size(path,1) > 0
            path = [path; r c row(2) col(2)];
            return
        end
    end
end

path = zeros(0,4);
end

%% - solver - - - -
% size(B)

W = zeros(0,4);

% make a sorted list of all pins
pin = sort(B(B>0),'descend');
npins = size(pin,1);
if npins < 1
    return
end

% pin, count, benefit
pincount = zeros(npins,3);
pincount(1,1) = pin(1);
k = 1;
count = 1;
for i = 2:npins
    if pin(i) == pincount(k,1)
        count = count + 1;
    else
        pincount(k,2) = count;
        k = k + 1;
        count = 1;
        pincount(k,1) = pin(i);
    end
end
pincount(k,2) = count;
pincount = pincount(1:k,:);
% calculate the benefit of a path
for i = 1:k
    if pincount(i,2) >= 2
        p = pincount(i,1);
        [row col] = find(B == p);
        d = 0;
        for j = 2:size(row,1);
            d = d + abs(row(j)-row(j-1)) + abs(col(j)-col(j-1));
        end
        pincount(i,3) = pincount(i,2)*p - d;
    end
end
[s ix] = sort(pincount(:,3),'descend');
pincount = pincount(ix,:);

% fprintf('pincount ...\n');
% pincount
% pause

for i = 1:k
    if pincount(i,2) >= 2
        [row col] = find(B == pincount(i,1));
        N = size(row,1);
        p = B(row(1),col(1));
        pinlist = [row(1) col(1)];
        npins = 1;
        for j = 2:N
            connected = false;
            link = npins;
            while ~connected && link >= 1
                rowx = row(j:N);
                colx = col(j:N);
                distance = abs(rowx - row(link)) + abs(colx - col(link));
                [d ix] = sort(distance,'ascend');
                if d(1) <= 20
                    row(j:N) = rowx(ix);
                    col(j:N) = colx(ix);

                    path = simplepath([row(link); row(j)], [col(link); col(j)], -p);
                    if size(path,1) > 0
        %                 fprintf('found path, p = %d, link = %d, j = %d\n', p, link, j);
                        W = [W ; path];
                        B = addwirepath(B,path,-p);
                        pinlist = [pinlist; row(j) col(j)];
                        npins = npins + 1;
                        connected = true;
                    end
                end
                link = link - 1;
            end
        end
    end
end

% fprintf('soln:\n');
% W
% pause
end

%%



%%
function B = addwirepath(B,path,label)
N = size(path,1);
for i = 1:N
    if B(path(i,1),path(i,2)) == 0
        B(path(i,1),path(i,2)) = label;
    end
    if B(path(i,3),path(i,4)) == 0
        B(path(i,3),path(i,4)) = label;
    end
end
end