Easy 101. Symmetric Tree

判断树是否是对称的
方法一：容易想到的递归方法

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

方法二：循环
层序遍历，使用队列

bool isSymmetric(TreeNode* root) {
        if(root == NULL) return true;
        std::queue<TreeNode*> q;
        TreeNode* t1 = new TreeNode();
        TreeNode* t2 = new TreeNode();
        q.push(root->left);
        q.push(root->right);
        while(!q.empty()){
            t1 = q.front();
            q.pop();
            t2 = q.front();
            q.pop();
            if(t1 == NULL && t2 == NULL) continue;
            if(t1 == NULL | t2 == NULL) return false;
            if(t1->val != t2->val) return false;
            q.push(t1->left);
            q.push(t2->right);
            q.push(t1->right);
            q.push(t2->left);
        }
        return true;
    }