617 合并二叉树

 

不修改原来树的结构

public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
    if (t1 == null) {
        return t2;
    }
    if (t2 == null) {
        return t1;
    }
    // 先合并根节点
    TreeNode root = new TreeNode(t1.val + t2.val);
    // 再递归合并左右子树
    root.left = mergeTrees(t1.left, t2.left);
    root.right = mergeTrees(t1.right, t2.right);
    return root;
}