LeetCode101 对称二叉树

给定一个二叉树，检查它是否是镜像对称的。

先创建一个镜像的二叉树，即交换二叉树的左右子树，然后比较二叉树的异同即可。

注意判断异同的时候origin和new都可能单独为nullptr，不要漏掉情况

/**
 * 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:
    bool isSymmetric(TreeNode* root) {
        TreeNode* symmetricTree=build_symmetric(root);
        return judge_same(root,symmetricTree);
    }

    bool judge_same(TreeNode* origin, TreeNode* symmetric){
        if(origin==nullptr)
            return symmetric==nullptr;
        if(symmetric==nullptr)
            return false;
        return origin->val==symmetric->val && judge_same(origin->left,symmetric->left)
        && judge_same(origin->right,symmetric->right);
    }

    TreeNode* build_symmetric(TreeNode* root){
        if(root==nullptr)
            return nullptr;
        TreeNode* newTree=new TreeNode(root->val);
        newTree->left=build_symmetric(root->right);
        newTree->right=build_symmetric(root->left);
        return newTree;
    }
};