two-sum-iv-input-is-a-bst.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) {
        Set<Integer> hashSet = new HashSet<>();
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        
        while(!queue.isEmpty()){
            TreeNode node = queue.remove();
            if(hashSet.contains(k - node.val))
                return true;
            hashSet.add(node.val);
            if(node.left != null)
                queue.add(node.left);
            if(node.right != null)
                queue.add(node.right);
        }
        return false;
    }
    }