LeetCode-653. Two Sum IV - Input is a BSTLevel up your coding skills and quickly land a job. This is the best place to expand your knowledge and get prepared for your next interview.https://leetcode.com/problems/two-sum-iv-input-is-a-bst/

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.

Example 1:

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

Example 2:

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

 

【C++】

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool findTarget(TreeNode* root, int k) {
        vector<int> nums;
        inOrder(root, nums);
        int i = 0, j = nums.size() - 1;
        while (i < j) {
            int sum = nums[i] + nums[j];
            if (sum == k) return true;
            if (sum < k) i++;
            else j--;
        }
        return false;
    }
    void inOrder(TreeNode* root, vector<int>& nums) {
        if(!root ) return;
        inOrder(root->left, nums);
        nums.push_back(root->val);
        inOrder(root->right, nums);
    }
};

【Java】

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean findTarget(TreeNode root, int k) {
        List nums = new ArrayList<>();
        inOrder(root, nums);
        int i = 0, j = nums.size() - 1;
        while (i < j) {
            int sum = nums.get(i) + nums.get(j);
            if (sum == k) return true;
            if (sum < k) i++;
            else j--;
        }
        return false;
    }
    void inOrder(TreeNode root, List nums) {
        if (root == null) return;
        inOrder(root.left, nums);
        nums.add(root.val);
        inOrder(root.right, nums);
    }
}

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