Java BFS, DFS iterative, DFS recursion 3 solutions


  • 1
    5

    It is a good question to review the three graph traversal methods.

    1. BFS

       public class Solution {
       public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
           if (node == null) {
               return null;
           }
           
           HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
           Queue<UndirectedGraphNode> queue = new LinkedList<>();
           UndirectedGraphNode root = new UndirectedGraphNode(node.label);
           map.put(node, root);
           queue.offer(node);
           
           while (!queue.isEmpty()) {
               int size = queue.size();
               for (int i = 0; i < size; i++) {
                   UndirectedGraphNode cur = queue.poll();
                   for (UndirectedGraphNode neighbor : cur.neighbors) {
                       UndirectedGraphNode newNeighbor = map.get(neighbor);
                       if (!map.containsKey(neighbor)) {
                           newNeighbor = new UndirectedGraphNode(neighbor.label);
                           map.put(neighbor, newNeighbor);
                           queue.offer(neighbor);
                       }
                       
                       map.get(cur).neighbors.add(newNeighbor);
                   }
               }
           }
           
           return root;
        }
       }
      
    2. DFS - recursion

        public class Solution {
        //dfs recursion 
        public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
           HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
           helper(map, node);
           return map.get(node);
        }
        
        private void helper(HashMap<UndirectedGraphNode, UndirectedGraphNode> map, 
            UndirectedGraphNode node) {
            if (node == null || map.containsKey(node)) {
                return;
            }
            
            map.put(node, new UndirectedGraphNode(node.label));
            
            for (UndirectedGraphNode neighbor : node.neighbors) {
                helper(map, neighbor);
                map.get(node).neighbors.add(map.get(neighbor));
            }
        }
        }
    
    1. DFS - iterative

       public class Solution {
       //dfs iterative 
       public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
           if (node == null) {
               return null;
           }
           
           HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
           Stack<UndirectedGraphNode> stack = new Stack<>();
           UndirectedGraphNode root = new UndirectedGraphNode(node.label);
           map.put(node, root);
           stack.push(node);
           
           while (!stack.isEmpty()) {
               UndirectedGraphNode cur = stack.pop();
               
               for (UndirectedGraphNode neighbor : cur.neighbors) {
                   if (!map.containsKey(neighbor)) {
                       UndirectedGraphNode temp = new UndirectedGraphNode(neighbor.label);
                       map.put(neighbor, temp);
                       stack.push(neighbor);
                   }
                   
                   map.get(cur).neighbors.add(map.get(neighbor));
               }
           }
           
           return root;
       }
       }

  • 0
    J

    These are some good solutions, just some thoughts on BFS here because I was doing BFS.

    1. it's good practice to specify the type of a generic class, i.e. LinkedList<UndirectedGraph>().
    2. in the while loop, you don't have to have a for loop over queue because you are already checking if it's empty. And it's very error-prone to modify a list when you are iterating over it.

    Hope this'll help.


Log in to reply
 

Looks like your connection to LeetCode Discuss was lost, please wait while we try to reconnect.