題目：

題解：

class Solution {
public:bool check(TreeNode *u, TreeNode *v) {queue <TreeNode*> q;q.push(u); q.push(v);while (!q.empty()) {u = q.front(); q.pop();v = q.front(); q.pop();if (!u && !v) continue;if ((!u || !v) || (u->val != v->val)) return false;q.push(u->left); q.push(v->right);q.push(u->right); q.push(v->left);}return true;}bool isSymmetric(TreeNode* root) {return check(root, root);}
};