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
/**
* 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;
HashSet map = new HashSet();
return checkk(root,k,map);
}
public boolean checkk(TreeNode root, int k,HashSet map){
if(root == null) return false;
if(map.contains(k-root.val)) return true;
map.add(root.val);
return checkk(root.left,k,map) || checkk(root.right,k,map);
}
}
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原文来源：《653. Two Sum IV – Input is a BST》
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