2021-6-22合并二叉树

已知两颗二叉树，将它们合并成一颗二叉树。合并规则是：都存在的结点，就将结点值加起来，否则空的位置就由另一个树的结点来代替。例如：

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param t1 TreeNode类 
     * @param t2 TreeNode类 
     * @return TreeNode类
     */
    public TreeNode mergeTrees (TreeNode t1, TreeNode t2) {
        // write code here
        if(t1==null)
            return t2;
        if(t2==null)
            return t1;
        if(t1==null &&t2==null)
            return null;
        t1.val=t1.val+t2.val;
        t1.left=mergeTrees(t1.left,t2.left);
        t1.right=mergeTrees(t1.right,t2.right);
        return t1;
    }
}