653. Two Sum IV - Input is a BST (Easy)

转载于 2017-09-12 15:28:00 发布 · 57 阅读

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原文链接：http://www.cnblogs.com/yancea/p/7510378.html

本文介绍了一种在二叉搜索树(BinarySearchTree,BST)中查找是否存在两个节点，其值相加等于给定目标值的方法。通过递归遍历BST，并采用辅助函数searchNumber进行查找，最终确定是否存在这样两个节点。

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

思路：递归遍历BST（Binary Search Tree）

class Solution:
    def findTarget(self, root, k):
        """
        :type root: TreeNode
        :type k: int
        :rtype: bool
        """
        self.root = root
        self.k = k
        return self.searchNumber(root)
        
    def searchNumber(self, root):
        if not root:
            return False
        node = self.root
        n = self.k - root.val
        if n != root.val:
            while node:
                if node.val == n:
                    return True
                if n > node.val:
                    node = node.right
                else:
                    node = node.left
        return self.searchNumber(root.left) or self.searchNumber(root.right)