How to build a graph from given string of pairs

I have an array of strings that represents the edges of a graph.

For example:

["6 11", "9 5", "11 9", "15 9", "13 15", "12 14", "15 16", "1 16"]  

Now I want to create a graph for this so I can see how many nodes are connected and how many are not connected. I am not sure what approach to follow for this.

I have used a Map in my program but I am not able to group the nodes properly in my code:

public static void process(int n, List<String> input) {      Map<Integer, Set<Integer>> map = new HashMap<>();      for (String in : input) {          String[] arr = in.split(" ");          int a1 = Integer.parseInt(arr[0]);          int a2 = Integer.parseInt(arr[1]);          int first = Math.min(a1, a2);          int second = Math.max(a1, a2);            if (map.size() == 0) {              Set<Integer> s = new HashSet<>();              s.add(first);              s.add(second);              map.put(first, s);              continue;          }            boolean found = false;          for (int k : map.keySet()) {              Set<Integer> set = map.get(k);                if (set.contains(first)) {                  map.get(k).add(second);                  found = true;                  break;              }              if (set.contains(second)) {                  map.get(k).add(first);                  found = true;                  break;              }          }          if (!found) {              Set<Integer> s = new HashSet<>();              s.add(first);              s.add(second);              map.put(first, s);          }      }      System.out.println(map);  }  

Now with this program I am getting a map with below values:

{5=[16, 1, 5, 9, 11, 13, 15], 6=[6, 11], 12=[12, 14]}  

The problem here is I already have 11 for map key = 5. So node 6 should be added to the set for key = 5 itself. So the map should look like this:

{5=[16, 1, 5, 9, 11, 13, 15, 6], 12=[12, 14]}  

How to do this, what approach I need to follow here? Here I used a map just for convenience because in a later step I wanted to count the size of each key means: 5 has 8 nodes, 12 has 2 nodes, etc. Nodes which are not having edges are 2, 3, 4, 7, 8, 10.

https://stackoverflow.com/questions/65745596/how-to-build-a-graph-from-given-string-of-pairs January 16, 2021 at 09:20AM