LeetCode 653: Two Sum IV - Input is a BST

Edge case:

need to determine whether two numbers come from same node.

/**
 * 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) {
        if (root == null) {
            return false;
        }
        
        return inorderAndSearch(root, root, k);
    }
    
    private boolean inorderAndSearch(TreeNode current, TreeNode root, int target) {
        if (current == null) {
            return false;
        }
        
        return inorderAndSearch(current.left, root, target) || findValue(root, target - current.val, current) || inorderAndSearch(current.right, root, target);
    }
    
    private boolean findValue(TreeNode root, int value, TreeNode current) {
        if (root == null) {
            return false;
        }
        
        return (root != current && root.val == value) || findValue(root.left, value, current) || findValue(root.right, value, current);
    }
}

 

 

/**
 * 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) {
        if (root == null) {
            return false;
        }
        
        List<Integer> nums = new ArrayList<>();
        inorder(root, nums);
        int start = 0;
        int end = nums.size() - 1;
        while (start < end) {
            if (nums.get(start) + nums.get(end) == k) {
                return true;
            } else if (nums.get(start) + nums.get(end) > k) {
                end--;;
            } else {
                start++;;
            }
        }
        return false;
    }
    
    private void inorder(TreeNode root, List<Integer> nums) {
        if (root == null) {
            return;
        }
        inorder(root.left, nums);
        nums.add(root.val);
        inorder(root.right, nums);
    }
}