深度优先搜索解决

C++ 代码

/**
 * 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:
    void mirror(TreeNode* root) {
        reverse(root);
    }
    void reverse(TreeNode* subroot){
        //递归完成，每次传入根节点使其左右子树翻转
        if(!subroot) return;
        //swap
        TreeNode* tmp;
        if(!subroot->left && !subroot->right);
        else{
            // cout << "val值是" <<subroot->val<<"子树被改变了"<<endl;
            tmp=subroot->left;
            subroot->left=subroot->right;
            subroot->right=tmp;
        }
        if(subroot->left) reverse(subroot->left); 
        if(subroot->right) reverse(subroot->right);
    }
    //问题1：子树没有传入
};