token alg step ab*+ ab*+ ab*+ (apop top two valuesy (bcompute or (cab*+ (aerror xxxxxx stack description push value of push value of push result ( of the multiplication pop top two valuesy xxxxxx only one value on stacktwo needed table the sequence of algorithm steps taken when evaluating the invalid postfix expression as the one illustrated in figure we can quickly find path from the starting point to the exit this usually involves scanning the entire maze and mentally eliminating dead ends but consider human size maze in which you are inside the maze and only have "rat' -eyeview you cannot see over the walls and must travel within the maze remembering where you have been and where you need to go in this situationit' not as easy to find the exit as compared to viewing the maze on paper an algorithm that can be used to find path through maze is likely to employ technique similar to what you would use if you were inside the maze in this sectionwe explore the backtracking technique to solving maze and design an algorithm to implement our technique figure sample maze with the indicated starting (sand exit (epositions backtracking the most basic problem-solving technique in computer science is the brute-force method it involves searching for solution to given problem by systematically trying all possible candidates until either solution is found or it can be determined there is no solution brute-force is time-consuming and is generally chosen as last resort but some problems can only be solved using this technique