Two Sum - LeetCode

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于 2015-03-24 20:11:12 发布

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分类专栏： python LeetCode LeetCode题解

本文链接：https://blog.youkuaiyun.com/u010006643/article/details/44597529

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本文针对LeetCode上的经典题目TwoSum提供了一种高效的解决方案。通过使用字典来存储数值及其索引，可以在O(n)的时间复杂度内找到两个数，使它们的和等于给定的目标值。该方法巧妙地避开了双重循环的低效搜索。

Two Sum - LeetCode

题目：

Given an array of integers, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.

You may assume that each input would have exactly one solution.

Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2

分析：

这道题利用的就是字典查找复杂度为O(1)的快速，避免了暴力查找的长时间。注意的是所给数组中有可能有两个一样的元素，但是字典中不会有重复元素，所以需要特殊处理和判断。

代码：

class Solution:
    # @return a tuple, (index1, index2)
    def twoSum(self, num, target):
        # if not issort(num):
            dic ={}
            length = len(num)
    
            for i in range(0,length):
                dic[num[i]] = i
            for i in dic.keys():
                if target - i in dic:
                    if dic[i] == dic[target - i]:
                        pre = num.index(i)
                        return pre+1, num.index(i,pre+1)+1
                    return min(dic[i]+1,dic[target - i]+1) , max(dic[i]+1,dic[target - i]+1)