617.Merge Two Binary Trees

Solution 1: On

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
        if(t1 == null && t2 == null){
            return null;
        }
        else if(t1 == null && t2 != null){
            return t2;
        }
        else if(t1 != null && t2 == null){
            return t1;
        }
        else {
            TreeNode newRoot = new TreeNode(t1.val+t2.val);
            newRoot.left = mergeTrees(t1.left, t2.left);
            newRoot.right = mergeTrees(t1.right, t2.right);
            return newRoot;
        }
    }
}