Introduction This is the list of modern CPP tricks often used in Coding Interviews and Competitive Programming. If you like Rachit's work, you can follow at - Discord - https://bit.ly/discord-rachit Programming YouTube Channel - https://bit.ly/rachityoutube Contents: No more nested min(x, min(y, ...)) JavaScript like Destructuring using Structured Binding in C++ Powerful Logging and Debugging How debug macros work? The Problem with this macro - its not scalable Solution using a powerful macro Generic Reader and Writer for multiple variables and containers Usage Decorators in C++ and Multiple Parameters Live Demo on YouTube Printing as many variables in one line Powerful decorator functions in C++ Exploiting decorators by nesting them Sets and Maps Tricks s.contains vs s.find(...) != s.end multiset.extract vs multiset.erase(multiset.find(...)) No more nested min(x, min(y, ...)) Use initializer list and std::min and std::max to make life easy small = min(x, min(y, min(z, k))); // the old way small = min({x, y, z, k}); // life is easy JavaScript like Destructuring using Structured Binding in C++ pair< int , int > cur = { 1 , 2 }; auto [x, y] = cur; // x is now 1, y is now 2 // no need of cur.first and cur.second array< int , 3 > arr = { 1 , 0 , - 1 }; auto [a, b, c] = arr; // a is now 1, b is now 0, c is now -1 Powerful Logging and Debugging How debug macros work? Straight to the point, I have often used the debug macro which stringifies the variable names and their values. # define deb ( x ) cout << #x << " " << x int ten = 10 ; deb (ten); // prints "ten = 10" This is often useful in debugging. The Problem with this macro - its not scalable However, when you have multiple variables to log, you end up with more deb2 and deb3 macros. # define deb ( x ) cout << #x << " " << x # define deb2 ( x ) cout << #x << " " << x << " " << #y << " " << y # define deb3 ( x, y, z ) cout << #x << " " << x << " " << #y << " " << y << " " << #z << " " << z This is not scalable. Solution using a powerful macro Here is the solution using variadic macros and fold expressions, # define deb (...) logger(#__VA_ARGS__, __VA_ARGS__) template < typename ...Args> void logger (string vars, Args&&... values) { cout << vars << " = " ; string delim = " " ; (..., (cout << delim << values, delim = " , " )); } int xx = 3 , yy = 10 , xxyy = 103 ; deb (xx); // prints "xx = 3" deb (xx, yy, xxyy); // prints "xx, yy, xxyy = 3, 10, 103" Generic Reader and Writer for multiple variables and containers template < typename ... T> void read (T &...args) { ((cin >> args), ...); } template < typename ... T> void write (string delimiter, T &&...args) { ((cout << args << delimiter), ...); } template < typename T> void readContainer (T &t) { for ( auto &e : t) { read (e); } } template < typename T> void writeContainer (string delimiter, T &t) { for ( const auto &e : t) { write (delimiter, e); } write ( " \n " ); } Usage // Question: read three space seprated integers and print them in different lines. int x, y, z; read (x, y, z); write ( " \n " , x, y, z); // even works with variable data types :) int n; string s; read (n, s); write ( " " , s, " has length " , n, " \n " ); // Question: read an array of `N` integers and print it to the output console. int N; read (N); vector< int > arr (N); readContainer (arr); writeContainer ( " " , arr); // output: arr[0] arr[1] arr[2] ... arr[N - 1] writeContainer ( " \n " , arr); /* * * output: * arr[0] * arr[1] * arr[2] * ... * ... * ... * arr[N - 1] */ Decorators in C++ and Multiple Parameters Live Demo on YouTube Check the online demo on YouTube here on Rachit's channel . Printing as many variables in one line template < typename ...T> void printer (T&&... args) { ((cout << args << " " ), ...); } int age = 25 ; string name = " Rachit " ; printer ( " I am " , name, ' , ' , age, " years old " ); // ^ This prints the following // I am Rachit, 25 years old Powerful decorator functions in C++ template < typename F> auto debug_func ( const F& func) { return [func]( auto &&... args ) { // forward reference cout << " input = " ; printer (args...); auto res = func (forward< decltype (args)>(args)...); cout << " res = " << res << endl; return res; }; } debug_func (pow)( 2 , 3 ); // ^ this automatically prints // input = 2 3 res = 8 Exploiting decorators by nesting them Lets define another decorator beautify as follows. template < typename F> auto beautify ( const F& func) { return [func]( auto &&... args ) { // forward reference cout << " ======== " << endl; func (forward< decltype (args)>(args)...); cout << " ======== " << endl; }; } beautify (debug_func(pow( 2 , 3 ))); // ^ this now prints // ======== // input = 2 3 res = 8 // ======== Its amazing how much you can do by writing such generic decorators and nest them. Think about decorators like log_time that calculates the time taken for a given function. Sets and Maps Tricks s.contains vs s.find(...) != s.end set<int> example{1, 2, 3, 4}; example.find(3) != example.end() // true example.contains(3) // true Note that this works with map as well as set . multiset.extract vs multiset.erase(multiset.find(...)) multiset<int> mset{1, 1, 2, 2, 3, 3}; mset.erase(1); // {2, 2, 3, 3} deleted all 1s mset.erase(mset.find(2)) // {2, 3, 3} need to use erase + find mset.extract(3) // {2, 3} simple and clean multiset::extract helps remove single instance naturally. Note this also works with normal set and map . It returns a node handle
