C++ std::vector::push_back Segmentation Fault on a very easy code

So what I'm trying to do is write a program that is a maze. After compiling, I'm getting the following message: Segmentation fault.

I have read tends of postings regarding this but I am still stuck. Do somebody of you know what is wrong with the code and how to avoid it? I would highly appreciate the comment/concern or any kind of opinion regarding it. Any advice or guess would be appreciated.

#ifndef A4_HPP
#define A4_HPP

#include "Maze.hpp"
#include <iostream>
#include <iostream>
#include <vector>
#include <set>


int distance(Maze& maze, int sx, int sy, int fx, int fy) {
    std::vector<int> D;

    if (sx == fx && sy == fy){
        return 0;
    }
    else {
        if (maze.is_open(sx + 1, sy) == true && maze.is_visited(sx + 1, sy) == false){
            int Dis1 = 1 + distance(maze, sx + 1, sy, fx, fy);
            maze.unmark(sx + 1, sy);
            maze.mark(sx + 1, sy);
            D.push_back(Dis1);
            return distance(maze, sx + 1, sy, fx, fy);

        }
        if (maze.is_open(sx, sy + 1) == true && maze.is_visited(sx, sy + 1) == false){
            int Dis2 = 1 + distance(maze, sx, sy + 1, fx, fy);
            maze.unmark(sx, sy + 1);
            maze.mark(sx, sy + 1);
            D.push_back(Dis2);
            return distance(maze, sx, sy + 1, fx, fy);

        }
        if (maze.is_open(sx - 1, sy) == true && maze.is_visited(sx - 1, sy) == false){
            int Dis3 = 1 + distance(maze, sx - 1, sy, fx, fy);
            maze.unmark(sx - 1, sy);
            maze.mark(sx - 1, sy);
            D.push_back(Dis3);
            return distance(maze, sx - 1, sy, fx, fy);

        }
        if (maze.is_open(sx, sy - 1) == true && maze.is_visited(sx, sy - 1) == false){
            int Dis4 = 1 + distance(maze, sx, sy - 1, fx, fy);
            maze.unmark(sx, sy - 1);
            maze.mark(sx, sy - 1);
            D.push_back(Dis4);
            return distance(maze, sx, sy - 1, fx, fy);

        }

        else {
            if (maze.is_open(sx, sy) == false){
                return 0;
            }
        }
    }
    return 0;
}

#endif // A4_HPP