LeetCode101-对称二叉树-递归-树-数据结构-迭代

原题链接

class Solution {
public:
    bool isSymmetric(TreeNode* root) {
        if(!root)   return true;
        return dfs(root -> left, root -> right);
    }

    bool dfs(TreeNode* l, TreeNode* r){
        if(l == NULL || r == NULL)  return l == NULL && r == NULL;
        else if(l -> val == r -> val)   return dfs(l -> left, r -> right) && dfs(l -> right, r -> left);
        return false;
    }
};

class Solution {
public:
    bool isSymmetric(TreeNode* root) {
        if(!root)   return true;
        queue q;
        q.push(root -> left), q.push(root -> right);
        while(q.size()){
            auto l = q.front();
            q.pop();
            auto r = q.front();
            q.pop();
            if(l && r && l -> val == r -> val){
                q.push(l -> left);
                q.push(r -> right);
                q.push(l -> right);
                q.push(r -> left);
            }
            else if(l == NULL && r != NULL || l != NULL && r == NULL)   return false;
            else if(l && r && l -> val != r -> val) return false;

        }

        return true;
    }
};