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
1 private boolean dfs(TreeNode root, HashSet<Integer> set, int k) 2 { 3 if (root == null) return false; 4 if (set.contains(k-root.val)) return true; 5 set.add(root.val); 6 return dfs(root.left,set,k) || dfs(root.right,set,k); 7 } 8 9 public boolean findTarget(TreeNode root, int k) { 10 HashSet<Integer> set = new HashSet<>(); 11 return dfs(root,set,k); 12 }
653. Two Sum IV - Input is a BST
原文：http://www.cnblogs.com/wzj4858/p/7710746.html