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) {
        // write code here
        TreeNode root=merge(t1,t2);
        return root;
    }

    protected TreeNode merge(TreeNode t1, TreeNode t2){
        TreeNode root=null;
        if(t1==null&&t2==null) return root;
        if(t1==null){
            root=new TreeNode(t2.val);
            root.left=merge(null,t2.left);
            root.right=merge(null,t2.right);
            return root;
        }
        else if(t2==null){
            root=new TreeNode(t1.val);
            root.left=merge(t1.left,null);
            root.right=merge(t1.right,null);
            return root;
        }
        else{
            root=new TreeNode(t1.val+t2.val);
        }

        root.left=merge(t1.left,t2.left);
        root.right=merge(t1.right,t2.right);

        return root;

    }
}