617_Merge_Two_Binary_Trees.java

class Solution {
    public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
        if (t1 == null && t2 == null) {
            return null;
        }

        int sum = 0;

        if (t1 != null) {
            sum += t1.val;
        }

        if (t2 != null) {
            sum += t2.val;
        }

        TreeNode tn = new TreeNode(sum);
        tn.left = mergeTrees(t1 == null ? null : t1.left, t2 == null ? null : t2.left);
        tn.right = mergeTrees(t1 == null ? null : t1.right, t2 == null ? null : t2.right);

        return tn;
    }
}