代码随想录：对称二叉树

代码随想录：对称二叉树

递归挺巧妙的，平时我肯定会用层次遍历，然后双指针看数组是否对称。

递归代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left),
 * right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {

        tra(root);
        return root;
    }

    void tra(TreeNode* target) {
        if (target != NULL) {
            TreeNode* temp = target->left;
            target->left = target->right;
            target->right = temp;
            tra(target->left);
            tra(target->right);
        }
    }
};