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 dummy = new TreeNode(0);
        dummy.left = t1;
        voidmerge(t1, t2);
        return dummy.left;
    }

    private void voidmerge(TreeNode t1, TreeNode t2) {
        if (t1 != null)
            //相加节点值
            t1.val += t2 != null ? t2.val : 0;
        else return;
        if (t1.left != null)
            //递归
            voidmerge(t1.left, t2 == null || t2.left == null ? null : t2.left);
        else
            //把t2挂到t1上
            t1.left = t2 == null || t2.left == null ? null : t2.left;

        if (t1.right != null)
            //递归
            voidmerge(t1.right, t2 == null || t2.right == null ? null : t2.right);
        else//把t2挂到t1上
            t1.right = t2 == null || t2.right == null ? null : t2.right;
    }
}