leetcode 101. Symmetric Tree

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本文介绍了一种算法来判断给定的二叉树是否是对称的，即树的左右子树是否镜像对称。

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

For example, this binary tree is symmetric:

But the following is not:

class Solution {
public:
	bool isSymmetric(TreeNode* root) {
		if (root == NULL)
			return true;
		vector<TreeNode*>que;
		que.push_back(root);
		while (!que.empty())
		{
			vector<TreeNode*>newque;
			for (int i = 0; i < que.size(); i++)
			{
				if (i < que.size() / 2)
				{
					if (que[i] == NULL&&que[que.size() - 1 - i] != NULL)
						return false;
					if (que[i] != NULL&&que[que.size() - 1 - i] == NULL)
						return false;
					if (que[i] != NULL&&que[que.size() - 1 - i] != NULL&&que[i]->val != que[que.size() - 1 - i]->val)
						return false;
				}
				if (que[i] != NULL)
				{
					newque.push_back(que[i]->right);
					newque.push_back(que[i]->left);
				}
			}
			que = newque;
		}
		return true;
	}
};