My enemy randomly paths away from player in maze-solving game

I have a maze generator that the player attempts to solve, and an enemy randomly spawns in the maze. It attempts to path towards the player and match their location index (in theory). In practice, however, it will move away from the player for extended periods before pathing back.

The code in question is the "if pR > enemyR; enemyR = enemyR + randi([0,2]);

In theory, this should move the enemy position down if the player is below and up if the player is above, same for left and right. Any ideas as to why it tends to wander off?

    function drawMaze(maze, playerRow, playerCol, goalPos, enemyPos)
        % Draw maze
        imagesc(maze);
        colormap("sky"); % Define colors
        axis equal tight off;
        % Draw player sprite
        hold on;
        plot(playerCol, playerRow, 'ko', 'MarkerSize', 9, 'MarkerFaceColor', 'k');
        %draw goal position
        plot(goalPos(1),goalPos(2),'bo', 'MarkerSize', 9);
        %draw enemy position
        plot(enemyPos(1),enemyPos(2),'ro','MarkerSize', 9, 'MarkerFaceColor', 'r');
        hold off;
        drawnow;
    end
    
    % Welcome Message
    welcomeMsg = 'Welcome to our game! Press OK to start. Use the arrow keys to move. Try to get to the bottom right!';
    gameStart = questdlg(welcomeMsg,'Start Game', 'OK','Cancel','Ok');
    
    % Start game
    if strcmp(gameStart,'OK')
        %Prompt player to select difficulty (map size)
        diffSelect = questdlg('Select a difficulty','Welcome','Easy','Medium','Hard','Medium');
        diff = 0; %initialize difficulty selection
        DC = 0; %initialie DC
                switch diffSelect
                    case 'Easy'
                        diff = 4;
                    case 'Medium'
                        diff = 5;
                    case 'Hard'
                        diff = 9;
                end
    
        map = mapMaze(2,1,'MapSize',[diff,diff],'MapResolution',diff); % create map
        mapMatrix = getOccupancy(map); % create an array from generated map
    
        startR = 0; % initialize starting index
        startC = 0;
    
        for c = size(mapMatrix,2):-1:1
            for r = 1:1:size(mapMatrix,1)
                if mapMatrix(r,c) == 0 % find first zero in top left
                    startR = r; % save as starting index
                    startC = c;
                    break
                end
            end
        end
    
        goal = [0,0]; %initialize goal
        for c = 1:1:size(mapMatrix,2)  %find last zero in bottom right
            for r = 1:1:size(mapMatrix,1)
                if mapMatrix(r,c) == 0
                    goal(1) = r;
                    goal(2) = c; % save as goal index
                end
            end
        end
    
        enemy = [0,0]; 
        enemy(1) = randi([1,size(mapMatrix,1)]); % randomly place enemy on map
        enemy(2) = randi([1,size(mapMatrix,2)]);
        while mapMatrix(enemy(1),enemy(2)) ~= 0 % if enemy is placed in wall
            enemy(1) = randi([1,size(mapMatrix,1)]); 
            enemy(2) = randi([1,size(mapMatrix,2)]); % re-do until placed in maze
        end
    
        pR = startR; % Player starting location
        pC = startC;
    
        fig = figure;
        drawMaze(mapMatrix, pR, pC, goal, enemy) % display initial map
    
        while true % Start game loop
            % Wait for user input
            keyPress = waitforbuttonpress;
            if keyPress == 0  % a mouse click
                continue;
            end
    
            newR = pR; % get current position
            newC = pC;
            enemyR = enemy(1);
            enemyC = enemy(2);
            %randomizer = [-1,0,0,1];
    
            key = fig.CurrentCharacter;
            switch key % Update player position based on input key pressed
                case 30 %up
                    newR = pR - 1;
                case 31 %down
                    newR = pR + 1;
                case 28 %left
                    newC = pC - 1;
                case 29 %right
                    newC = pC + 1;
                end
    
            %check if new position is valid
            if newR >= 1 && newR <= size(mapMatrix, 1) && ...
                    newC >= 1 && newC <= size(mapMatrix, 2) && ...
                    mapMatrix(newR, newC) == 0
                % if valid, update player position
                pR = newR;
                pC = newC;
            end
    
            if pR > enemyR % if player is below enemy, move down
                enemyR = enemyR + randi([0,2]);
            elseif pR < enemyR % if player is above enemy, move up 
                enemyR = enemyR - randi([0,2]);
            end
    
            if pC > enemyC % if player is right of enemy, move right
                enemyC = enemyC + randi([0,2]);
            elseif pC < enemyC % if player is left of enemy, move left
                enemyC = enemyC - randi([0,2]);
            end
    
            if enemyR >= 1 && enemyR <= size(mapMatrix, 1) && ...
                    enemyC >= 1 && enemyC <= size(mapMatrix, 2)
                enemy(1) = enemyR;
                enemy(2) = enemyC;
            end
    
            % check if player has reached the goal
            if pR == goal(1) && pC == goal(2)
                win = questdlg('You win! Would you like to play again?','Congratulations!','Yes','No','Yes');
                if strcmp(win,'Yes')
                    diffSelect = questdlg('Select a difficulty','Welcome','Easy','Medium','Hard','Medium');
                    switch diffSelect
                        case 'Easy'
                            diff = 4;
                        case 'Medium'
                            diff = 5;
                        case 'Hard'
                            diff = 9;
                    end
                    map = mapMaze(2,1,'MapSize',[diff,diff],'MapResolution',diff);
                    mapMatrix = getOccupancy(map);
                    pR = startR;
                    pC = startC;
                    for c = 1:1:size(mapMatrix,2)
                        for r = 1:1:size(mapMatrix,1)
                            if mapMatrix(r,c) == 0
                                goal(1) = r;
                                goal(2) = c; % save as goal index
                            end
                        end
                    end
                    for c = size(mapMatrix,2):-1:1
                        for r = 1:1:size(mapMatrix,1)
                            if mapMatrix(r,c) == 0 % find first zero in top left
                                startR = r; % save as starting index
                                startC = c;
                                break
                            end
                        end
                    end
                else
                    break
                end
            end
            drawMaze(mapMatrix,pR,pC, goal, enemy)
        end
    end
    

Answer 1

[Umeshraja]

Hi @John,

I assume that the enemy always take the shortest path and takes moves only one step at a time. The core issue lies in enemy movement logic and the current limitation in your code are

• Direct Movement: The enemy moves directly towards the player without considering walls, which can lead to it getting stuck or moving away when there's no valid direct path.
• Path Direction: The horizontal and vertical movements are handled separately, which can result in zigzag patterns or inefficient paths.

To improve this, we can implement a more efficient algorithm such as Breadth-First Search (BFS). BFS takes maze walls into account and finds valid paths around obstacles, ensuring the enemy always takes the shortest path while moving one step at a time.

In this script, the player is represented in black, the goal is blue, and the enemy is red. Please refer to the attached file for implementation details.

Hope it helps!