Leetcode二叉搜索树习题集

98. Validate Binary Search Tree

class Solution {
public:
    bool isValidBST(TreeNode* root) {
        return dfs(root,NULL,NULL);
    }
    
　　// 此处要最大最小是因为BST需要比较的是全局的最大最小
    bool dfs(TreeNode* root, TreeNode* Min, TreeNode* Max){
        if(root==NULL) return true;
        if(Min!=NULL && Min->val>=root->val) return false;
        if(Max!=NULL && Max->val<=root->val) return false;
        return dfs(root->left,Min,root) && dfs(root->right,root,Max);
    }
};

 

100. Same Tree

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

 

700. Search Tree

class Solution {
public:
    TreeNode* searchBST(TreeNode* root, int val) {
        if(root==NULL) return NULL;
        if(root->val == val)
            return root;
        else if(root->val < val)
            return searchBST(root->right,val);
        else 
            return searchBST(root->left,val);
    }
};

 

701. Insert Node

class Solution {
public:
    TreeNode* insertIntoBST(TreeNode* root, int val) {
        if(root==NULL)
            return new TreeNode(val); // 如果找到合适的位置，直接在此处新建一个节点
        if(root->val<val)
            root->right = insertIntoBST(root->right,val);
        else
            root->left = insertIntoBST(root->left,val);
        return root;
    }
};

 

Delete Node

class Solution {
public:
    TreeNode* deleteNode(TreeNode* root, int key) {
        if(root==NULL) return NULL;
        if(root->val == key){
            // 如果只有一个节点或者直接没有节点了
            if(root->left==NULL) return root->right;
            if(root->right==NULL) return root->left;
            // 如果两个子节点都有，找到右数的最小节点拿过来删
            TreeNode* minNode = getMin(root->right);
            root->val = minNode->val;
            // 替换完值后再右数继续删除最小的那个值
            root->right = deleteNode(root->right,minNode->val);
        } else if(root->val > key){
            root->left = deleteNode(root->left,key);
        } else {
            root->right = deleteNode(root->right,key);
        }
        return root;
    }
    
    TreeNode* getMin(TreeNode* node){
        while(node->left!=NULL) 
            node = node->left;
        return node;
    }
};