Leetcode 653. sum of two IV - input BST

Title Description

653. Sum of two numbers IV - Input BST

solution ： Depth first

Create a hash table , Record the traversed node value , At the same time, find out whether there is and equal to in the hash table k The elements of

/** * 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:
    unordered_set<int> hash_table;
    bool findTarget(TreeNode* root, int k) {
    
        if (root == nullptr) return false;

        if (hash_table.count(k - root->val)) return true;
        hash_table.insert(root->val);
        return findTarget(root->left, k) || findTarget(root->right, k);
    }
};