https://github.com/rachitiitr/modern-cpp-tricks
Modern CPP Tricks often useful in Coding Interviews and Competitive Programming
https://github.com/rachitiitr/modern-cpp-tricks
coding-interviews competitive-programming cpp tips-and-tricks
Last synced: 7 months ago
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Modern CPP Tricks often useful in Coding Interviews and Competitive Programming
- Host: GitHub
- URL: https://github.com/rachitiitr/modern-cpp-tricks
- Owner: rachitiitr
- Created: 2021-06-01T19:36:32.000Z (over 4 years ago)
- Default Branch: main
- Last Pushed: 2024-03-16T07:29:56.000Z (over 1 year ago)
- Last Synced: 2025-03-28T09:06:18.838Z (7 months ago)
- Topics: coding-interviews, competitive-programming, cpp, tips-and-tricks
- Homepage:
- Size: 10.7 KB
- Stars: 705
- Watchers: 14
- Forks: 62
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
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README
## 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, ...))`](#no-more-nested-minx-miny-)
- [JavaScript like Destructuring using Structured Binding in C++](#javascript-like-destructuring-using-structured-binding-in-c)
- [Powerful Logging and Debugging](#powerful-logging-and-debugging)
- [How debug macros work?](#how-debug-macros-work)
- [The Problem with this macro - its not scalable](#the-problem-with-this-macro---its-not-scalable)
- [Solution using a powerful macro](#solution-using-a-powerful-macro)
- [Generic Reader and Writer for multiple variables and containers](#generic-reader-and-writer-for-multiple-variables-and-containers)
- [Usage](#usage)
- [Decorators in C++ and Multiple Parameters](#decorators-in-c-and-multiple-parameters)
- [Live Demo on YouTube](#live-demo-on-youtube)
- [Printing as many variables in one line](#printing-as-many-variables-in-one-line)
- [Powerful decorator functions in C++](#powerful-decorator-functions-in-c)
- [Exploiting decorators by nesting them](#exploiting-decorators-by-nesting-them)
- [Sets and Maps Tricks](#sets-and-maps-tricks)
- [`s.contains` vs `s.find(...) != s.end`](#scontains-vs-sfind--send)
- [`multiset.extract` vs `multiset.erase(multiset.find(...))`](#multisetextract-vs-multiseterasemultisetfind)
## No more nested `min(x, min(y, ...))`
Use initializer list and `std::min` and `std::max` to make life easy
```cpp
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++
```cpp
pair cur = {1, 2};
auto [x, y] = cur;
// x is now 1, y is now 2
// no need of cur.first and cur.second
array 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.
```cpp
#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.
```cpp
#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,
```cpp
#define deb(...) logger(#__VA_ARGS__, __VA_ARGS__)
template
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
```cpp
template
void read(T &...args) {
((cin >> args), ...);
}
template
void write(string delimiter, T &&...args) {
((cout << args << delimiter), ...);
}
template
void readContainer(T &t) {
for (auto &e : t) {
read(e);
}
}
template
void writeContainer(string delimiter, T &t) {
for (const auto &e : t) {
write(delimiter, e);
}
write("\n");
}
```
### Usage
```cpp
// 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 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](https://www.youtube.com/watch?v=ZhWyNjPGXD4).
### Printing as many variables in one line
```cpp
template
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++
```cpp
template
auto debug_func(const F& func) {
return [func](auto &&...args) { // forward reference
cout << "input = ";
printer(args...);
auto res = func(forward(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.
```cpp
template
auto beautify(const F& func) {
return [func](auto &&...args) { // forward reference
cout << "========" << endl;
func(forward(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 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 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