题解 | #合并二叉树#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param t1 TreeNode类 
     * @param t2 TreeNode类 
     * @return TreeNode类
     */
    public TreeNode mergeTrees (TreeNode t1, TreeNode t2) {
        
        // 如果两个节点都为空则返回null
        if(t1==null&&t2==null){
            return null;
        }else{
            //创建新节点
            TreeNode res=null;
            //左子树为空，新节点复制右子树
            if(t1==null){
                res=new TreeNode(t2.val);
                res.left=mergeTrees(null,t2.left);
                res.right=mergeTrees(null,t2.right);
            }else if(t2==null){
            //右子树为空，新节点复制左子树
                res=new TreeNode(t1.val);
                res.left=mergeTrees(t1.left,null);
                res.right=mergeTrees(t1.right,null);
            }else{
            //都不为空，根节点相加，左右节点便利
                res=new TreeNode(t1.val+t2.val);
                res.left=mergeTrees(t1.left,t2.left);
                res.right=mergeTrees(t1.right,t2.right);
            }
        return res;
        }
        
    }
}