Find least common ancestor of two nodes in java

Question

I have looked at a lot of other answers on stackoverflow and can't find anything that works, I either get the root, or node1 itself returned, I'm not sure how to do this recursively and have tried it many times all ending the same way. Any help would be greatly appreciated!

Here's my code:

private static Node findLCA(Node node1, Node node2) {
    Node temp1 = node1, temp2 = node2, currentLargest = null;
    int largestDepth = 0;
    boolean found = false;
    if(node1 == null || node2 == null){
        return null;
    } else{
        while(found == false){
            if(temp1.getParent() != null && temp2.getParent() != null && temp1.getParent() == temp2.getParent() && nodeDepth(temp1.getParent()) > largestDepth){
                largestDepth = nodeDepth(temp1.getParent());
                currentLargest = temp1;
                temp1 = temp1.getParent();
                temp2 = temp2.getParent();
            } else if(temp1.getParent() != null){
                temp1 = temp1.getParent();
            } else if(temp2.getParent() != null){
                temp2 = temp2.getParent();
            }
            if(temp1.getParent() == null && temp2.getParent() == null){
                found = true;
            }

        }
        if(nodeDepth(temp1) >= largestDepth){
            return temp1;
        } else{
            return currentLargest;
        }
    }
}

I edited it to make a list of ancestors of each node, but I'm not sure how to go around checking each one to see if the elements in the list's match up since they are usually different sizes.

Heres the new code:

ArrayList<PhyloTreeNode> list1 = new ArrayList<PhyloTreeNode>();
    ArrayList<PhyloTreeNode> list2 = new ArrayList<PhyloTreeNode>();

    if(node1 == null || node2 == null){
        return null;
    } else{
        if(node1.getParent() != null){
            list1.add(node1.getParent());
            findLeastCommonAncestor(node1.getParent(), node2);
        }
        if(node2.getParent() != null){
            list2.add(node2.getParent());
            findLeastCommonAncestor(node1, node2.getParent());
        }
    }

Answer 1

We can use recursive post order traversal for computing lowest common ancestor, Here is my Java implementation Here a & b are given input data for which i have to find lowest common ancestors.

public static int lowestcommanancestors(Node root,int a,int b){
 if(root==null)
  return 0;
 int x=lowestcommanancestors(root.left,a,b);
 int y=lowestcommanancestors(root.right,a,b);
 if(x+y==2){
  System.out.println(root.getData());
  return 0;
 }
 if(root.getData()==a || root.getData()==b){
  return x+y+1;
 }
 else{
  return x+y;
 }
 
}

First i am checking whether given input node presenting in left subtree or not,if yes just return 1 else 0,Similarly for right sub tree.When sum becomes 2 first time that node will be lowest common ancestors. Tell me if i am wrong or you are getting difficulties to understanding the code