class Solution:
def twoSum(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[int]
"""
nums_length = len (nums)
index_1 = int ()
index_2 = int ()
target_list = []
for x in range (nums_length):
second_num = target - nums[x]
if second_num != nums[x]:
if second_num in nums:
index_2 = nums.index(second_num)
index_1 = x
break
elif second_num in nums[x+1::]:
index_2 = nums[x+1::].index(second_num)+x +1
index_1 = x
break
target_list = [index_1, index_2]
return target_list

The concept in this solution:

1. have the first number,

2. second_number = target – first_number

3. check whether the second_number in list.

4. if not, then move to next number in the list

5. if yes, check whether the first number and the second number is the same: if it is the same, then make sure it is two different numbers , but starting a new list nums[x+1 ::], and then find the index in the new list. The important thing here is: for the new list starting index is not “0”, it should be “x+1”!!

6. if the second number is not the first number ,then it is easy to just identify the index.

Lesson learned:

**1. how to use the value to identify the index: list_name.index(the_value)**

2. the second list starting index for nums[x+1::] is x+1 , for example nums[x+1::] [y], then the original index is (x+1) +y

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