1.Two Sum Leetcode Python

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

这道题目来自于introduction to algorithm书上，介绍的是brute force的用法。

这里我们采用hashtable 将数值即为key value为index 将target-num[index]作为搜索条件。 类似的题目还有4 sum

代码如下：

class Solution:
    # @return a tuple, (index1, index2)
    def twoSum(self, num, target):
        process={}
        for index in range(len(num)):
            if target-num[index] in process:
                return [process[target-num[index]]+1,index+1]
            process[num[index]]=index