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) {
        mergeTrees1(t1, t2);
        return t1;
    }

    static public void mergeTrees1(TreeNode t1, TreeNode t2) {
        if (t1 == null || t2 == null) {
            return;
        }
        t1.val = t1.val + t2.val;
        if (t1.left == null && t2.left != null) {
            t1.left = t2.left;
            t2.left = null;
        }
        if (t1.right == null && t2.right != null) {
            t1.right = t2.right;
            t2.right = null;
        }
        if (t1.left != null) {
            mergeTrees1(t1.left, t2.left);
        }
        if (t1.right != null) {
            mergeTrees1(t1.right, t2.right);
        }
    }
}