我正在研究树问题 Convert Sorted Array to Binary Search Tree - LeetCode
Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.
Example:
Given the sorted array: [-10,-3,0,5,9], One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST: 0 / \ -3 9 / / -10 5
直观的 D&Q 解决方案是
class Solution:
def sortedArrayToBST(self, nums: List[int]) -> TreeNode:
"""
Runtime: 64 ms, faster than 84.45%
Memory Usage: 15.5 MB, less than 5.70%
"""
if len(nums) == 0: return None
#if len(nums) == 1: return TreeNode(nums[0])
mid = len(nums) // 2
root = TreeNode(nums[mid])
if len(nums) == 1: return root
if len(nums) > 1:
root.left = self.sortedArrayToBST(nums[:mid])
root.right = self.sortedArrayToBST(nums[mid+1:])
return root
mid
设置为 len(nums)//2
或 (low + high)//2
当阅读其他提交的内容时,我发现
class Solution:
def sortedArrayToBST(self, nums: List[int]) -> TreeNode:
return self.buildBST(nums, 0, len(nums))
def buildBST(self, nums, left, right):
if right <= left:
return None
if right == left + 1:
return TreeNode(nums[left])
mid = left + (right - left) // 2
root = TreeNode(nums[mid])
root.left = self.buildBST(nums, left, mid)
root.right = self.buildBST(nums, mid + 1, right)
return root
mid
设置为 mid = low + (high -low)//2
mid = low + (high -low)//2
相对于 (low + high)//2
有何优势?
最佳答案
这是一种避免整数溢出的模式;该代码可能是从具有固定大小整数的语言移植的。当索引变得与用于包含它们的类型一样大时,中间 low + high
值的溢出就会成为问题,导致未定义的行为、不正确的结果和漏洞。 (当您是 searching something that’s not an array 时,这种情况甚至会发生在像 size_t
这样的大整数类型上。)
…但是在Python中,不存在整数溢出,所以你是对的,你可以做(low + high)//2
。
关于python - `mid = low + (high -low)//2` 比 `(low + high)//2` 有什么好处?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/55611990/