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
只要是两数之和的题，一定要记得用哈希表来做，这道题只不过是把数组变成了一棵二叉树而已
/**
* 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;
}
Set<Integer> set = new HashSet<>();
Queue<TreeNode> queue =new LinkedList<>();
queue.add(root);
while(!queue.isEmpty()){
TreeNode node = queue.poll();
if(set.contains(node.val)){
return true;
}
set.add(k-node.val);
if(node.left != null){queue.add(node.left);}
if(node.right != null){queue.add(node.right);}
}
return false;
}
}