653. Two Sum IV - Input is a BST

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653. Two Sum IV - Input is a BST

Description

Given the root of a binary search tree and an integer k, return true if there exist two elements in the BST such that their sum is equal to k, or false otherwise.

Example 1:

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Input: root = [5,3,6,2,4,null,7], k = 9
Output: true

Example 2:

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Input: root = [5,3,6,2,4,null,7], k = 28
Output: false

Constraints:

  • The number of nodes in the tree is in the range [1, 10^4].
  • -10^4 <= Node.val <= 10^4
  • root is guaranteed to be a valid binary search tree.
  • -10^5 <= k <= 10^5

Hints/Notes

Solution

Language: C++

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/**
* 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> inorder;

    bool findTarget(TreeNode* root, int k) {
        dfs(root);
        int l = 0, r = inorder.size() - 1;
        while (l < r) {
            if (inorder[l] + inorder[r] == k) {
                return true;
            } else if (inorder[l] + inorder[r] > k) {
                r--;
            } else {
                l++;
            }
        }
        return false;
    }

    void dfs(TreeNode* root) {
        if (!root) {
            return;
        }
        if (root->left) dfs(root->left);
        inorder.push_back(root->val);
        if (root->right) dfs(root->right);
    }
};