leetcode679

LeetCode 题目 679 可能是指“两数之和 III - 数据结构设计”(Two Sum III - Data Structure Design)。这是一个数据结构题，要求设计一个支持添加、删除元素以及查找两个整数是否存在目标和的数据结构。具体来说，你需要实现一个名为 `TargetSum` 的类：

class TargetSum:
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.nums = []  # 用列表存储所有数字
        self.sum_map = {}  # 使用哈希表 (字典) 存储每个数字的补数及其索引

    def add(self, num: int) -> None:
        """
        Adds a new element into the data structure.
        :param num: An integer
        :return: None
        """
        self.nums.append(num)
        if num in self.sum_map:
            self.sum_map[num].append(len(self.nums)-1)
        else:
            self.sum_map[num] = [len(self.nums)-1]

    def remove(self, val: int) -> None:
        """
        Removes a number from the data structure.
        :param val: An integer
        :return: None
        """
        index_to_remove = self.find_index(val)
        if index_to_remove is not None:
            self.nums.pop(index_to_remove)
            for key, indices in self.sum_map.items():
                if index_to_remove in indices:
                    indices.remove(index_to_remove)

    def find(self, target: int) -> bool:
        """
        Returns if there exists any pair of numbers which sum up to the given target.
        :param target: An integer
        :return: True if such pair exists, False otherwise.
        """
        return self.has_pair(target)

    def has_pair(self, target: int) -> bool:
        """
        Internal method used by find() to check for a pair using binary search on nums.
        """
        left, right = 0, len(self.nums)-1
        while left < right:
            current_sum = self.nums[left] + self.nums[right]
            if current_sum == target:
                return True
            elif current_sum < target:
                left += 1
            else:
                right -= 1
        return False