1. Two Sum

The problem is called "Two Sum" with array, so I decided to solve with Python. 

Description:

Problem Description from https://leetcode.com/problems/two-sum/description/

 

Solution:

Code from me

When I looked into the each variables, I used nested loop(two for loop) to find out the two variables in the array. And if the sum of two variables equal to the value of target, I return the i and j as a dictionary.

 

Brute Force: 

Time complexity: O(N^2)

Space complexity: O(1)

 

Solution2:

Using Hash map, you can use only one loop for searching the variables in arrary

source from https://bortfolio.tistory.com/122

Let's say the Target - nums[i] is a nums[x]. nums[x] would be an another interger we should find. Using example 1, the first value of vals is 7. Before putting second value (which is 9 - 7 = 2), 7 is already in the vals. Therefore, the array[0] and array[1] would be the two sum of intergers we tried to find. 

 

* index(nums[i]) return the location of nums[i], so it would be "0" in this case.

 

Time complexity: O(N)

Space complexity: O(N)