Introduction
This is the list of modern CPP tricks often used in Coding Interviews and Competitive Programming.
1. 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
2. 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
3. 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 debug(x) cout << #x << " " << x
int ten = 10;
debug(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 debug(x) cout << #x << " " << x
#define debug2(x) cout << #x << " " << x << " " << #y << " " << y
#define debug3(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 debug(...) 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;
debug(xx); // prints "xx = 3"
debug(xx, yy, xxyy); // prints "xx, yy, xxyy = 3, 10, 103"
4. 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]
*/
5. Decorators in C++ and Multiple Parameters
Printing as many variables in one line
template<typename ...T>
void printer(T&&... args) {
((cout << args << " "), ...);
}
int age = 25;
string name = "Apurv";
printer("I am", name, ',', age, "years old");
// ^ This prints the following
// I am Apurv, 22 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
// ========
It's 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.
6. Using a Template
Using a template is one of the best ideas to speed up your implementation. Keep your template ready that has your macros written in them already. This helps in reducing a lot of your time which otherwise would have gone in writing the whole code from scratch. I use the following template, you can use one that suits you.
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef pair<int,int> pi;
#define F first
#define S second
#define PB push_back
#define MP make_pair
#define REP(i,a,b) for (int i = a; i < b; i++)
#define fastIO() ios_base::sync_with_stdio(0), cin.tie(0)
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");
}
#define debug(...) logger(#__VA_ARGS__, __VA_ARGS__)
template<typename ...Args>
void logger(string vars, Args&&... values) {
cout << vars << " = ";
string delim = "";
(..., (cout << delim << values, delim = ", "));
}
const int MAX = 5E5 + 5;
const int MOD = 1E9 + 7;
void solve(){
int tt;
cin>>tt;
while(tt--){
// Your code goes here
}
}
int main(){
fastIO();
solve();
}
Thank you for reading, please let me know if you have some possible improvements or addition.
You can now extend your support by buying me a Coffee.😊👇
