653 Two Sum IV - Input is a BST
Problem
Given a Binary Search Tree and a target number, return true if there exist two elements in the BST such that their sum is equal to the given target.
Example 1:
Input:
5
/ \
3 6
/ \ \
2 4 7
Target = 9
Output: True
Example 2:
Input:
5
/ \
3 6
/ \ \
2 4 7
Target = 28
Output: False
Solutions:
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public boolean findTarget(TreeNode root, int k) {
HashSet<Integer> appr = new HashSet<Integer>();
return inorder(root, k, appr);
}
private boolean inorder(TreeNode node, int k, HashSet<Integer> appr) {
if (node == null) {
return false;
}
if (inorder(node.left, k, appr)) {
return true;
}
if (appr.contains(k - node.val)) {
return true;
}
appr.add(node.val);
if (inorder(node.right, k, appr)) {
return true;
}
return false;
}
}