合并两个二叉树

Question

I want to merge a tree with another tree, t. If there is overlapping data, I want to add them together. This is my code right now. I don't understand how to do this merge function with only parameter t. Doesn't merge usually have two parameters?

public class TreeFunctions {

   private TreeNode root;

   public TreeFunctions(TreeNode root) {
        this.root = root;
   }

   public TreeNode merge(TreeNode t) {
        TreeNode curr = this.root;
        if (curr == null) {
            return t;
        }

        if (t == null) {
            return curr;
        }

        curr.data += t.data;
        curr.left = merge(t.left);
        curr.right = merge(t.right);
        return curr;
   }
}

public class TreeNode{
    TreeNode left;
    TreeNode right;
    int data;

    public TreeNode(int data) {
        this.data = data;
    }
    public TreeNode(int data, TreeNode left, TreeNode right) {
        this.data = data;
        this.left = left;
        this.right = right;
    }

    public static String inOrder(TreeNode a) {
        if(a == null) return "";
        else return inOrder(a.left).trim() + " " + a.data + " " + inOrder(a.right).trim();
    }
}

EDIT My tests for merge:

public void testMerge2() {
        TreeFunctions c = new TreeFunctions(new TreeNode(5, new TreeNode(2), null));
        TreeNode d = new TreeNode(2, new TreeNode(2), new TreeNode(1));
        TreeNode res2 = c.merge(d);
        assertEquals(TreeNode.inOrder(res2).trim(), "4 7 1");
    }

public void testMerge3() {
        TreeFunctions c = new TreeFunctions(new TreeNode(5, new TreeNode(2), null));
        TreeNode res2 = c.merge(null);
        assertEquals(TreeNode.inOrder(res2).trim(), "2 5");
    }

public void testMerge4() {
        TreeFunctions c = new TreeFunctions(new TreeNode(1, new TreeNode(2, new TreeNode(5), null), null));
        TreeNode res2 = c.merge(new TreeNode(1, null, new TreeNode(2, null, new TreeNode(5))));
        assertEquals(TreeNode.inOrder(res2).trim(), "5 2 2 2 5");
    }

Answer 1

I've edited my answer per your responses. I believe this is what you want.Please try it and let me know.

In the code, function goes down one level for both t1 and t2 so that merge always takes place on the same level and the same side (left-left/right-right).

 public TreeNode merge(TreeNode t) {
        TreeNode curr = this.root; 
        merge2(curr,t);
        return curr;
   }
   public  void merge2(TreeNode t1,TreeNode t2) {
        if(t2==null)
            return;
        t1.data += t2.data;
        if(t2.left!=null)
        {
            if(t1.left==null)
                t1.left = new TreeNode(0);
            merge2(t1.left,t2.left);
        }
        if(t2.right!=null)
        {
            if(t1.right==null)
                t1.right = new TreeNode(0);
            merge2(t1.right,t2.right);
        }

   }