101. Symmetric Tree

bool isSymmetric(TreeNode* root) {
if(!root) return true;
return isSymmetric(root->left,root->right);
}
bool isSymmetric(TreeNode* left,TreeNode* right){
if(!left&&!right) return true;
if((left&&!right)||(!left&&right)||(left->val!=right->val)) return false;
return isSymmetric(left->left,right->right)&&isSymmetric(left->right,right->left);
}

bool isSymmetric(TreeNode* root) {
if(!root) return true;
queue<TreeNode*> q1,q2;
q1.push(root->left);
q2.push(root->right);
while(!q1.empty()&&!q2.empty()){
TreeNode*node1=q1.front();
TreeNode*node2=q2.front();
q1.pop();
q2.pop();
if((node1&&!node2)||(!node1&&node2))
return false;
if(node1){
if(node1->val!=node2->val) return false;
q1.push(node1->left);
q1.push(node1->right);
q2.push(node2->right);
q2.push(node2->left);
}
}
return true;
}