Two Sum IV - Input is a BST Problem & Solution

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.

C++ Solution

``````#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops")
#pragma GCC optimization("max-inline-insns-recursive-auto")

static const int _=[](){ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();

/**
* 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:
bool findTarget(TreeNode* root, int k) {
return findTarget(root, root, k);
}

private:
bool findTarget(TreeNode* root, TreeNode* node, int k) {
if (node == nullptr) {
return false;
}

return findNode(root, node, k - node->val) ||
findTarget(root, node->left, k) ||
findTarget(root, node->right, k);
}

bool findNode(TreeNode* root, TreeNode* node, int k) {
while (root != nullptr) {
if (root != node &&
root->val == k) {
return true;
}

if (k < root->val) {
root = root->left;
} else {
root = root->right;
}
}

return false;
}
};
``````