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:

    1
   / \
  2   2
 / \ / \
3  4 4  3
But the following [1,2,2,null,3,null,3] is not:
    1
   / \
  2   2
   \   \
   3    3

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

还是使用递归来判断是否镜面对称。比较简单。
先判断根节点，然后调用上题的算法来判断左右子树是否相同。

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