%Copyright 2006, Adarsh Krishnamurthy (me.berkeley.edu/~adarsh) and Athulan Vijayaraghavan (me.berkeley.edu/~athulan)

clc; clear all;
%recursive backtracker
tic
%size of the maze - only square
maze_size = 20;

n_cells = maze_size*maze_size;

%listing all the cells with a uid in an array
k = 1;
for i = 1:maze_size
    for j = 1:maze_size
        corners = corner_pts([j i])';
        cells(k, :) = [k corners(:)'];
        k = k + 1;    
    end
end

%listing all the edges with a uid in an array
edges = [];
k = 1;
for i = 1:maze_size-1
    for j = 1:maze_size
        edges(k, :) = [k i j-1 i j];
        edges(k+1, :) = [k+1 j-1 i j i];
        k = k + 2;
    end
end

%list all the edges for the cells
for i = 1:size(cells, 1)
    cell_col = [cells(i,2) cells(i,3); cells(i,4) cells(i,5); cells(i,6) cells(i,7); cells(i,8) cells(i,9)];
    k = 2;
    cell_edges(i, 1) = i;
    for j = 1:size(edges, 1)
        edge_col = [edges(j,2) edges(j,3); edges(j,4) edges(j,5)];
        if (ismember(edge_col, cell_col, 'rows')==[1;1])
            cell_edges(i, k) = j;
            k = k+1;
        end
    end
end

%initialize the cell stack
stack = [];

%choose a random cell to begin with
r = ceil(length(cells)*(rand));
stack(1) = r;
visited = stack;
cells(r, :) = [];

 

ctr = 1;

while length(stack)>0
    stack;
    visited;
    current_cell = stack(end);
    current_neighbors = neighbors2d(current_cell(1), maze_size);
    for i = 1:length(current_neighbors)
        if ismember(current_neighbors(i), visited)
            current_neighbors(i) = 0;
        end
    end
    current_neighbors(find(current_neighbors==0))=[];
    
    if length(current_neighbors)==0
        stack(end) = [];
    elseif length(current_neighbors>0)        
        r = ceil(length(current_neighbors)*(rand));
        chosen_neighbor = current_neighbors(r);
        common_edge = intersect(cell_edges(chosen_neighbor, 2:5), cell_edges(current_cell, 2:5));
        common_edge(find(common_edge==0))=[];
        
        edges(find(edges(:, 1)==common_edge), :)=[];
        stack(end+1) = chosen_neighbor;
        visited(end+1) = chosen_neighbor;
    end
    
    ctr = ctr + 1
end
show_maze(maze_size, edges);
ctr