leetcode-617. 合并二叉树

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
        // 对 t1 节点进行判空，若该节点为空则直接返回 t2 的对应节点
        if (t1 == null) {
            return t2;
        }
        // 对 t2 节点进行判空，若该节点为空则直接返回 t1 的对应节点
        if (t2 == null) {
            return t1;
        }
        // 定义新的根节点为两棵树的根节点的和
        TreeNode merged = new TreeNode(t1.val + t2.val);
        // 新定义的树的所有左子树分别为 t1 和 t2 各自对应的左子树的和
        merged.left = mergeTrees(t1.left, t2.left);
        // 新定义的树的所有右子树分别为 t1 和 t2 各自对应的右子树的和
        merged.right = mergeTrees(t1.right, t2.right);
        // 返回最终合并完的二叉树
        return merged;
    }
}