Leetcode 270. Closest Binary Search Tree Value

Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the target.

Note:

• Given target value is a floating point.
• You are guaranteed to have only one unique value in the BST that is closest to the target.

沿着root向下找即可，每次判段一下是在root左边还是右边。注意没有child的情况。

 # Definition for a binary tree node.
 # class TreeNode(object):
 #     def __init__(self, x):
 #         self.val = x
 #         self.left = None
 #         self.right = None

 class Solution(object):
     def closestValue(self, root, target):
         """
         :type root: TreeNode
         :type target: float
         :rtype: int
         """
         #if target == root.val:
         #    return root.val

         if target < root.val:
             if not root.left:
                 return root.val
             else:
                 c1 = self.closestValue(root.left, target)
                 if abs(c1 - target) < abs(root.val - target):
                     return c1
                 else:
                     return root.val
         else:
             if not root.right:
                 return root.val
             else:
                 c2 = self.closestValue(root.right, target)
                 if abs(c2 - target) < abs(root.val - target):
                     return c2
                 else:
                     return root.val