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
        return order(t1, t2);
    }

    private TreeNode order(TreeNode t1, TreeNode t2) {
        if (t1 == null && t2 == null) {
            return null;
        }

        int val1 = t1 == null ? 0 : t1.val;
        int val2 = t2 == null ? 0 : t2.val;
        int val = val1 + val2;
        TreeNode node = new TreeNode(val);
        TreeNode leftNode = order(t1 == null ? null : t1.left, t2 == null ? null : t2.left);
        TreeNode rightNode = order(t1 == null ? null : t1.right, t2 == null ? null : t2.right);
        node.left = leftNode;
        node.right = rightNode;
        return node;
    }
}