Today I was solving this problem, INCPR04 Problem - CodeChef, I implemented a solution with O(length of the array) time complexity. But I was getting TLE. Then I looked up at some of the accepted solutions, their logic was same as mine, but they have added these statements:
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
I have tried doing the same and added these statements to my code and the solution got accepted. But I don’t exactly know what do these statements do. I have searched it on google and opened the first link but I couldn’t a get a lucid idea of what it is exactly doing. Could someone please elaborate what these statements actually do?
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ios_base::sync_with_stdio(false);
I will try to answer this question best of my experience and learning .
In CPP programs you can use both C and CPP style I/O but when you set the ios_base::sync_with_stdio (by default its value is true and synchronization is there, meaning they are sharing same buffers and you will get expected results if you use both C and CPP style I/O) to false it disables the synchronization between the C and C++ standard streams and std::cin becomes faster.
Now, because scanf() works faster than std::cin(), competitive coders use “ios_base::sync_with_stdio(false);” at the beginning of their main() to get faster input (and it really does make a big difference). Also I would like you to go through these links i provided below, they are from stack overflow.
Links :-
Using scanf() in C++ programs is faster than using cin?
Significance of ios_base::sync_with_stdio(false); cin.tie(NULL);
I hope I was able to answer your question 
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Thanks a lot, it really helped!
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will this optimization always happen in cpp program i.e can i use these lines for every cpp program?