LeetCode 101 Symmetric Tree

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree ​​[1,2,2,3,4,4,3]​​ is symmetric:

 

But the following ​​[1,2,2,null,3,null,3]​​ is not:

 

Note:
Bonus points if you could solve it both recursively and iteratively.

 

题解：递归比较二者的子树

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
bool ju(struct TreeNode* a,struct TreeNode* b){
      if(a->val == b->val)
      {
          if((a->left==NULL&&b->right==NULL)||(a->left!=NULL&&b->right!=NULL&&ju(a->left,b->right)))
          {
              if((b->left==NULL&&a->right==NULL)||(b->left!=NULL&&a->right!=NULL&&ju(b->left,a->right)))
                  return true;
              else
                  return false;
          }
          else
              return false;
         
      }
    return false;
}
bool isSymmetric(struct TreeNode* root) {
    
    if(root==NULL) return true;
    if((root->left==NULL&&root->right==NULL)||(root->left!=NULL&&root->right!=NULL&&ju(root->left,root->right)))
        return true;
    else
       return false;
    
}