9/23刷题合并二叉树

1.合并二叉树

思路一：DFS

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        if (t1 == nullptr) {
            return t2;
        }
        if (t2 == nullptr) {
            return t1;
        }
        TreeNode *merge=new TreeNode(t1->val+t2->val);//根节点
        merge->left=mergeTrees(t1->left,t2->left);//左子树递归
        merge->right=mergeTrees(t1->right,t2->right);//右子树递归
        return merge;
    }
};