又见递归

重点理解递归哈

第一阶段的代码

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param pRoot TreeNode类 
     * @return TreeNode类
     */
    TreeNode* Mirror(TreeNode* pRoot) {
        // write code here
        if(pRoot){
            //switch the child
            TreeNode *t = Mirror(pRoot->left);

            //update new chile with chile with iteration
            pRoot->left = Mirror(pRoot->right);//2句话合成一句话
            pRoot->right =t;
            
        }
        return pRoot;
    }
    
    TreeNode* Mirror2(TreeNode* pRoot) {
        // write code here
        if(pRoot){
            //switch the child
            TreeNode *t = pRoot->left;
            pRoot->left = pRoot->right;
            pRoot->right = t;
            //update new chile with chile with iteration
            pRoot->left = Mirror(pRoot->left);
            pRoot->right =Mirror(pRoot->right);
            
        }
        return pRoot;
    }
    
    
};