leetcode 第一题 two sum

最新推荐文章于 2022-02-15 12:11:10 发布

原创最新推荐文章于 2022-02-15 12:11:10 发布 · 107 阅读

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博客指出存在低效率问题，提出使用dict可提高效率，涉及信息技术领域的数据结构运用。

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"""
    Time Complexity = O(N^2)
    Space Complexity = O(1)

    Given an array of integers, return indices of the two numbers such that they add up to a specific target.
    You may assume that each input would have exactly one solution, and you may not use the same element twice.

    Example:
    Given nums = [2, 7, 11, 15], target = 9,
    Because nums[0] + nums[1] = 2 + 7 = 9,
    return [0, 1].
"""

低效率

class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        for i in nums:
            j = target - i
            tmp_nums_start_index = nums.index(i) + 1
            tmp_nums = nums[tmp_nums_start_index:]
            if j in tmp_nums:
                return [nums.index(i), tmp_nums_start_index + tmp_nums.index(j)]

if __name__ == '__main__':
    print(Solution().twoSum((2, 7, 11, 15), 17))

使用dict提高效率

class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        dict={}
        for i in range(len(nums)):
            if target-nums[i] not in dict:
                dict[nums[i]]=i
            else:
                return[dict[target-nums[i]],i]

if __name__ == '__main__':
    print(Solution().twoSum((2, 7, 11, 15), 17))