Solved! Leetcode 1214. Two Sum BSTs

source: https://leetcode.com/problems/two-sum-bsts/

Two Sum BSTs

Description

Given the roots of two binary search trees, root1 and root2, return true if and only if there is a node in the first tree and a node in the second tree whose values sum up to a given integer target.

Example 1:

Input: root1 = [2,1,4], root2 = [1,0,3], target = 5
Output: true
Explanation: 2 and 3 sum up to 5.

Example 2:

Input: root1 = [0,-10,10], root2 = [5,1,7,0,2], target = 18
Output: false

Constraints:

The number of nodes in each tree is in the range [1, 5000].
-109 <= Node.val, target <= 109

Solution

/**
 * 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 twoSumBSTs(TreeNode root1, TreeNode root2, int target) {
        return helper(root1, root2, target);
    }

    private boolean helper(TreeNode node1, TreeNode node2, int target){
        if(node1 == null || node2 == null)
            return false;
        int sum = node1.val + node2.val;
        if(sum == target){
            return true;
        }
        boolean ans = false;
        if(sum < target){
            ans = helper(node1, node2.right, target) || helper(node1.right, node2, target);
        } else {
            ans = helper(node1.left, node2, target) || helper(node1, node2.left, target);
        }
        return ans;
    }
}

/**

* 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 twoSumBSTs(TreeNode root1, TreeNode root2, int target) {

return helper(root1, root2, target);

}

private boolean helper(TreeNode node1, TreeNode node2, int target){

if(node1 == null || node2 == null)

return false;

int sum = node1.val + node2.val;

if(sum == target){

return true;

}

boolean ans = false;

if(sum < target){

ans = helper(node1, node2.right, target) || helper(node1.right, node2, target);

} else {

ans = helper(node1.left, node2, target) || helper(node1, node2.left, target);

}

return ans;

}

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