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• Title Description
• Their thinking
• The source code to share
• Learning summary
• The articles ---- Good article recommends

Title Description

Title Description
Given N Plus sign 、M A minus sign and N + M + 1 It's an integer , Xiao Ming wants to know at all by this N Plus sign 、MM A minus sign and N + M +1 It's legal to round it up In the suffix expression , Which is the biggest result ？
Please output this maximum result .
For example, using 1 2 3 + -, be “2 3 + 1 -” The result of this suffix expression is 4, It's the biggest .

Input description
The first line contains two integers N , M

The second line contains N + M + 1 It's an integer A .

Output description
Output an integer , For the answer .

I/o sample
Example
Input
1 1
1 2 3
Output
4

 Operation limit
Maximum operation time ：1s
Maximum running memory : 256M

Their thinking

At the beginning of this topic , We are also confused , How to discuss ± Parenthesized question , I have changed the example for several times and can't think of it , Until I found out Alex_996 It dawned on me , Here, I have learned from the experience of big men ：2019 The 10th Blue Bridge Cup in - Provincial competition - C/C++ university B Group - I. Postfix expression

• This question should first be clear , The input data can have negative numbers , This requires us to + perhaps - Consider the question of parentheses , How can we maximize the sum of the data we require .
• The first is No, - Number When , Just sum the input data directly ;
• When Yes - Number When it appears , Let's take an example to observe ：a1 < a2 < a3 < a4 < a5 < a6.
• One "-“ Number ：(a1 + a2 + a3) - (a4 + a5 + a6)
  Two ”-“ Number ：(a1 + a2 + a3) - (a4 + a5) - a6
  Three ”-“ Number ：(a1 + a2 + a3) - a4 - a5 - a6
  four ”-“ Number ：(a1 + a2） - （a4 - a3) - a5 - a6
  Five ”-" Number ：a1 - (a5 - a2） - （a4 - a3) - a6
  We can find a magical thing , Top ones 5 All the formulas are equal , Are equivalent to a1 + a2 + a3 - a4 - a5 - a6. So in short , That is, when we only need to discuss a minus sign, we can solve all the problems of minus signs ！
• 1. If all numbers are positive ： that (a2 + a3 + a4 + a5 + a6) - (a1) Is the biggest result
  2. If all numbers are negative ： that (a6) - (a1 + a2 + a3 + a4 + a5) Is the biggest result , Equivalent to (abs(a1) + abs(a2) + abs(a3) + abs(a4) + abs(a5)) - abs(a6), With the first 1 Kind of similar .
  3. If there are positive and negative , that (a1 + a2 + a3) - (a4 + a5 + a6), among a1、a2、a3 Positive number ,a4、a5、a6 It's a negative number , Is the biggest result , Equivalent to (a1 + a2 + a3) + abs(a4) + abs(a5) + abs(a6)
• So let's summarize ： 1. If all numbers are positive ： final a6 - a1 Equivalent to abs(a1 - a6)2. If all numbers are negative , It's also abs(a1) - abs(a6), Equivalent to abs(a1 - a6)3. If there are positive and negative ： yes a1 + abs(a6), Equivalent to a1 - a6, It must be a positive number , So you can also add the absolute value number ：abs(a1 - a6)

The source code to share

# Time : 2022/2/21 14:41
# File : Postfix expression .py
# Author : yes Dream ah ！
# VX : Xu18300396393
# Ten thousand times sad , There will still be Dream, I've been waiting for you in the warmest place ！
N,M = map(int,input().split())
list1 = list(map(int,input().split()))
if M == 0:
print(sum(list1))
else:
sum = 0
list1.sort()
for i in range(1,N+M):
sum += abs(list1[i])
sum += abs(list1[-1]-list1[0])
print(sum)

Learning summary

• Assign values to multiple variables in a single line ：N,M = map(int,input().split())
• Summarizing the rules will make a very complex subject very simple ！

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