315. 计算右侧小于当前元素的个数 python

最新推荐文章于 2024-01-24 17:09:20 发布

clelouch

最新推荐文章于 2024-01-24 17:09:20 发布

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分类专栏： LeetCode

本文链接：https://blog.youkuaiyun.com/clelouch/article/details/80394665

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本文介绍了一种利用二叉搜索树实现的算法，并针对相同数值处理进行了优化，确保了在处理包含重复元素的列表时能正确计算每个元素后的小于它的元素数量。

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利用二叉搜索树

class Tree:
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None
        self.num = 1


class Solution:
    def countSmaller(self, nums):
        """
        :type nums: List[int]
        :rtype: List[int]
        """
        def insert(root, val):
            if root.val < val:
                if root.right is not None:
                    root.right = insert(root.right, val)
                else:
                    root.right = Tree(val)
            else:
                if root.left is not None:
                    root.num += 1
                    root.left = insert(root.left, val)
                else:
                    root.num += 1
                    root.left = Tree(val)
            return root

        n = len(nums)
        if n == 0:
            return []
        root = Tree(nums[-1])
        ret = [0]
        for i in range(n - 2, -1, -1):
            root = insert(root, nums[i])
            cnt = 0
            pointer = root
            while pointer.val != nums[i]:
                if pointer.val > nums[i]:
                    pointer = pointer.left
                else:
                    cnt += pointer.num
                    pointer = pointer.right
            ret.append(cnt)
        return ret[::-1]

在样例出错，主要原因是二叉树中出现相同的数字时候，判别出错

nums = [26,78,27,100,33,67,90,23,66,5,38,7,35,23,52,22,83,51,98,69,81,32,78,28,94,13,2,97,3,76,99,51,9,21,84,66,65,36,100,41]

改进之后，代码

class Tree:
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None
        self.num = 1


class Solution:
    def countSmaller(self, nums):
        """
        :type nums: List[int]
        :rtype: List[int]
        """
        def insert(root, val, temp):
            if root.val < val:
                temp += root.num
                if root.right is not None:
                    root.right, temp = insert(root.right, val, temp)
                else:
                    root.right = Tree(val)
            else:
                root.num += 1
                if root.left is not None:
                    root.left, temp = insert(root.left, val, temp)
                else:
                    root.left = Tree(val)
            return root, temp

        n = len(nums)
        if n == 0:
            return []
        root = Tree(nums[-1])
        ret = [0]
        for i in range(n - 2, -1, -1):
            root, num = insert(root, nums[i], 0)
            ret.append(num)
        return ret[::-1]