验证二叉搜索树 leetcode_二叉树 面试题

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题解

1. 递归

/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode() : val(0), left(nullptr), right(nullptr) {} * TreeNode(int x) : val(x), left(nullptr), right(nullptr) {} * TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {} * }; */
class Solution { 
   
public:
    vector<int>res;
    bool dfs(TreeNode *p,TreeNode *q){ 
   
        if(p != NULL && q != NULL){ 
   
            if(p->val == q->val && dfs(p->left,q->right) && dfs(p->right,q->left))return true;
        }
        else if(p == NULL && q == NULL)return true;
        return false;
    }
    bool isSymmetric(TreeNode* root) { 
   
        return dfs(root,root);
    }
};

2. 迭代

/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode() : val(0), left(nullptr), right(nullptr) {} * TreeNode(int x) : val(x), left(nullptr), right(nullptr) {} * TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {} * }; */
class Solution { 
   
public:
    queue<TreeNode *>q;
    bool isSymmetric(TreeNode* root) { 
   
        q.push(root),q.push(root);
        TreeNode *left,*right;
        while(!q.empty()){ 
   
            left = q.front();
            q.pop();
            right = q.front();
            q.pop();
            if(left != NULL && right == NULL || left == NULL && right != NULL)return false;
            if(left != NULL && right != NULL && left->val != right->val)return false;
            if(left == NULL)continue;
            q.push(left->left),q.push(right->right);
            q.push(left->right),q.push(right->left);
        }
        return true;
    }
};