牛客BM33. 二叉树的镜像

题目大意：给定一个二叉树，将其变换为源二叉树的镜像。

算法标签：递归

/*
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    TreeNode* Mirror(TreeNode* root) {
        if(root == NULL)
            return root;
        // 交换左右子树
        TreeNode* temp = root -> left;
        root -> left = root -> right;
        root -> right = temp;
        
        // 左右子树分别镜像一下
        root -> left = Mirror(root -> left);
        root -> right = Mirror(root -> right);
        
        return root;
    }
};