### Reverse Integer

Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: 123
Output: 321
Example 2:

Input: -123
Output: -321
Example 3:

Input: 120
Output: 21
Note:
Assume we are dealing with an environment which could only hold integers within the 32-bit signed integer range. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

```class Solution:
def reverse(self, x):
"""
:type x: int
:rtype: int
"""
list_x = []
if x >0 :
for str_x in str(x).split():
list_x.append(str_x)

r_list_x = list_x[::-1]
for item in list_x:
r_str_x =  "".join(item)
return (int (r_str_x))
```

What is wrong with this one:
x = 123,

str(x).split() is still “123”

split is split the spaces…

### two sum V3

```class Solution:
def twoSum(self, nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[int]
"""
dic_value_index = {}
index_1 = int ()
index_2 = int ()
for index, value in enumerate(nums):
dic_value_index [value] = index
for item in nums:
sec_num = target - item
if sec_num in dic_value_index:
if nums.index(item) != dic_value_index[sec_num]: # if they are not the same number
index_1 = nums.index(item)
index_2 = dic_value_index[sec_num]
break
return ([index_1, index_2])
```

Key of this solution:
1. enumerate (list_name) will walk through the index and the value;
2. put the value and index into the dictinary
3. search whether the sec_num in the dictionary (only key can be searched? )
4. if yes, the the value is the index of the sec_num
5. check whether the sec_num is actually the first number, if not , then return the index.

### Two Sum V2

```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

### Leetcode Two Sum – solution – V1

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 + nums = 2 + 7 = 9,
return [0, 1].

```

My first version:

```nested two for loops, find the two value sum == target

```

My second version:

also two loops: the first loop is the same, but the second loop starts from x+1, no need to start index 0.

### how to save all the received message to a file

1. create a list, data []

2. define a function, to send commands, and receive the response, then append the response to the list

def srp (s, send, recv=”recv”, wait = 2):
send = s.send(“{}\n”.format (send))
time.sleep(wait)
recv = s.recv(5000000)
data.append(recv)
return recv

3. you can execute some commands and put all in the list

srp (s, “conf t”)
srp (s, “interface loop 111”)
srp (s, “ip address x.x.x.x/32”)
srp (s, “no shut”)

4. write the list to a file

f = open (“SWAN_install_uninstall_logs.txt”, “w”)
for line in data:
f.write (“{}\n”.format(line))
f.close()

### how to insert a local time to Python programmer and use it

imort time

t = str (time.strftime(“%Y%m%d–%H%M%S”))

then you can use the string t

for example:

filename = backup + “-” + t

### how to read a txt file and perform action based on the contents of the file

f = open (“device_list.txt”, “r”)

for lines in f:

ip = lines.strip (“\n”)

Then you can do something with the ip