101. symmetrical binary tree (deep search)

Iteration is impossible iterative

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     bool flag = true; //判断标志
13     bool isSymmetric(TreeNode* root) {
14         if (!root) return 1;
 15          DFS (directory root-> left, directory root-> right);
 16          return In Flag;
 . 17      }
 18 is      void DFS (L * the TreeNode, the TreeNode * R & lt) {
 . 19          IF (R & lt In Flag || L &&!!!) Return ; / / prune 
20 is          the else  IF (L-L || R & lt ||> Val = the R-> Val!!!) { // Analyzing asymmetric 
21 is              In Flag = to false ;
 22 is              return ;
 23 is          }
 24          DFS (L-> left, the R-> right); // symmetrical search comparator 
25          DFS (L-> right, the R->left);    
26     }
27 };