LeetCode--Merge Two Binary Trees

Ideas:

    Select one of the trees, and if the corresponding two nodes are not null, add the values. In this way, the left side is traversed first, and then the right side is traversed.

/**
 * 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){
            return t2;
        }
        if(t2==null){
            return t1;
        }
        t1.val+=t2.val;
        t1.left=mergeTrees(t1.left,t2.left);
        t1.right=mergeTrees(t1.right,t2.right);
        return t1;        
    }
}