LeetCode-101. Symmetric Tree

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.

题目：给定一棵树，看是否对称

思路：我的思路是先看是不是空树和只有一个根节点，之后写个compare（）函数来判断左右节点是否相同。

class Solution {
public:
	 bool compare(TreeNode* p,TreeNode* q)
    {
    	if(!p&&!q)	
    		return true;
    	else if((!p&&q)||(p&&!q))
    		return false;
    	else if(p->val!=q->val)
			return false;
		return 	compare(p->left,q->right)*compare(p->right,q->left);	
	}
    bool isSymmetric(TreeNode* root) {
        TreeNode *p=root;
        if(p==NULL)
        	return true;
        TreeNode* root_left=root->left;
		TreeNode* root_left=root->right;	
		return compare(root_left,root_left);
    }
};