Problem Statement

Pattern:

Solution

HashSet<Integer> set = new HashSet<>();
 
public boolean findTarget(TreeNode root, int k) {
	if(root == null) return false;
	
	boolean left = findTarget(root.left, k);
	if(set.contains(k-root.val)) return true;
	set.add(root.val);
	boolean right = findTarget(root.right, k);
	
	return left || right;
}

final int s = 10000;
boolean[] vis = new boolean[s*2+2];
 
public boolean findTarget(TreeNode root, int k) {
	if(root == null) return false;
	
	boolean left = findTarget(root.left, k);
	if(Math.abs(k-root.val) <= s && vis[k-root.val+s]) return true;
	vis[root.val+s] = true;
	boolean right = findTarget(root.right, k);
	
	return left || right;
}

Solution with O(h) space