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Two Sum IV - Input is a BST

Problem​

Given the root of a Binary Search Tree and a target number k, return true if there exist two elements in the BST such that their sum is equal to the given target.

Solution Approach​

Expected Time complexity: O(n)O(n)

Click - to see solution code
class Solution {
   public:
    set<int> s;
    bool findTarget(TreeNode* root, int k) {
        if (root == nullptr) return false;
        int f = k - root->val;
        if (s.find(f) != s.end()) {
            return true;
        } else {
            s.insert(root->val);
            s.insert(f);
        }
        bool l = findTarget(root->left, k);
        bool r = findTarget(root->right, k);
        if (l || r) return true;
        return false;
    }
};