Recursive for find shortest path using DFS in maze in java

Question

`I got stack overflow error when using this code. i want it work if we already found the shortest path, then the recursive code will stop. the maze is contain character '#' and ' '. and if i found the shortest path, the path will mark with '.' please help thank you.

public static int getCoordinateY(String location){ //to get x coordinate
    String y = location.substring(2, 4);
    int coor = (y.charAt(0) - 'Q') * 10 + Character.getNumericValue(y.charAt(1));`enter code here`
    return coor;
    }
public boolean canPass(int y,int x) { //you can keep going if you not found # and .
    if(map[y][x] == '#' || map[y][x] == '.' ) {
        return false;
    }
    return true;
}
public Character[][] cloneArray(Character[][] src) { //copy array
    int length = src.length;
    Character[][] target = new Character[length][src[0].length];
    for (int i = 0; i < length; i++) {
        System.arraycopy(src[i], 0, target[i], 0, src[i].length);
    }
    return target;
}
public void finish(int x,int y){ //goal
    xgoal=x; 
    ygoal=y;
}
public int getDistance(){ //shortest distance from shortest path
    return finalDistance;
}
public void shortestPathStart(int xStart,int yStart, int xEnd, int yEnd){
    set('S',xStart,yStart); //start coordinate
    finish(xEnd,yEnd);
    shortestPathRec(xStart+1,yStart,0,map);//to right
    shortestPathRec(xStart-1,yStart,0,map);// to left
    shortestPathRec(xStart,yStart+1,0,map);//to up
    shortestPathRec(xStart,yStart-1,0,map);// to down
    map = result; //final map with '.'
    set('F',xEnd,yEnd);
    print();
}
public void shortestPathRec(int x,int y,int step,Character[][] map){
    if(canPass(x,y)){
        step++;
        Character[][] temp = cloneArray(map);
        temp[x][y] = '.'; //in the maze, '.' using for flags
        if(x == xgoal && y == ygoal){//if already found the goal
            hasDone = true;
            finalDistance = step;
            result = temp;
            return;
        }
        if(hasDone==true && finalDistance<step){ //if shortest path is found other path should be in this condition
            return;
        }
        shortestPathRec(x+1,y,step,temp);//calltherecursive again
        shortestPathRec(x-1,y,step,temp);
        shortestPathRec(x,y+1,step,temp);
        shortestPathRec(x,y-1,step,temp);
    }
}

If you get a stack overflow then you are probably recursing too deeply. For a problem such as this, that probably means you are not correctly detecting and avoiding loops in your path. Look carefully at your `canPass()` method, which seems intended to help with this, and at your `shortestPathRec()` method. How might it be that `canPass()` is not preventing you from looping? — John Bollinger, Apr 28 '17 at 18:52

score 0 · Answer 1 · answered Apr 28 '17 at 18:57

0

PROBLEM ANALYSIS

You fail to guard against physical backtracking: you move to a wall, but instead of backing up in your call stack (undo the last move), you go to the next recursion call and do the opposite move -- taking a second useless step instead of backing up to 0 useless steps. Your code will infinitely walk between those two squares until you exceed the stack limit.

REPAIR

Madify your code so that you never walk to a square you've already visited on this path. This is easy enough to research on line; Dijkstra's Algorithm is one of the earliest general solutions.

AVOIDANCE

Learn basic debugging. Among other things, insert print statements at entry and exit to each routine, printing the input parameters and return values. For extra clarity, keep an depth counter and indent the prints appropriately.

answered Apr 28 '17 at 18:57

Prune

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thank you so much for your answer. i'm trying to make backtrack but failed. can you give me an example to backtrack? I'm confuse with Dijkstra's Algorithm. – Anne Apr 29 '17 at 02:49
There are thousands of examples on the Internet. Exactly how and where are you confused? – Prune May 01 '17 at 16:04
Also, please remember the Stack Overflow guidelines. Among other things, this is a site for *specific* programming questions. When this gets to "I don't understand backtracking", you need research and a perhaps a local tutor, not SO. – Prune May 01 '17 at 16:06

Recursive for find shortest path using DFS in maze in java

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