Graph problems

Print all paths from vertex $v_0$ to vertex $v_1$

Q1. How to store a graph A1. We can use HashMap to store a vertex and all its children Create Edge class to store two vertexes Convert list of Edges to HashMap

    class Edge{
        String beg;
        String end;
        public Edge(String beg, String end){
            this.beg = beg;
            this.end = end;
        }
    }

    Map < String, Set < String>> map = new HashMap<>();

    public static Map < String, Set < String>> geneGraph(List < Edge> ls){
        Map> map = new HashMap<>();
        for(Edge e : ls){
            var set = map.get(e.beg);
            if( set == null){
                set = new HashSet<>();
            }
            set.add(e.end);
            map.put(e.beg, set);
        }
        return map;
    }

Print all paths from vertex a to vertex b

    public static void printAllPath(Map <String, Set <String>> map, String a, String b, List < String> ls){
        Set set = map.get(a); 
        if(set != null){
            for(String e : set){
                if( e != b){
                    printAllPath(map, e, b, append(ls, e));
                }else{
                    pl("");
                    List rs = append(ls, e);
                    printList(rs);
                }
            }
        }
    }

Find the longest path from vertex a to vertex b

    public static int printAllPathShortest(Map<String, Set<String>> map, String a, String b, List<String> ls){
        Set<String> set = map.get(a); 
        int max = Integer.MIN_VALUE;
        if(set != null){
            for(String e : set){
                if( e != b){
                    // Overflow in Integer here
                    int n = printAllPathShortest(map, e, b, append(ls, e)) + 1;
                    if(n > max){
                        max = n;
                    }
                }else{
                    List<String> rs = append(ls, e);
                    printList(rs);
                    return 0;
                }
            }
        }
        return max; 
    }