95 lines
2.5 KiB
Text
95 lines
2.5 KiB
Text
---
|
|
id: shorten-cpp
|
|
title: Shortening C++ Code
|
|
author: Benjamin Qi
|
|
description: How to make your code (un?)readable.
|
|
---
|
|
|
|
## Introduction
|
|
|
|
<resources>
|
|
<resource source="CPH" title="1.4 - Shortening Code" starred>Read before checking code below.</resource>
|
|
<resource source="GFG" url="cc-preprocessors" title="Macros"></resource>
|
|
<resource source="GCC" url="https://gcc.gnu.org/onlinedocs/cpp/Macros.html" title="Online Docs - Macros">reference</resource>
|
|
</resources>
|
|
|
|
## [My Template](https://github.com/bqi343/USACO/blob/master/Implementations/content/contest/template.cpp)
|
|
|
|
Some comments about specific parts:
|
|
|
|
### Pairs
|
|
|
|
```cpp
|
|
typedef pair<int,int> pi;
|
|
|
|
#define mp make_pair
|
|
#define f first
|
|
#define s second
|
|
```
|
|
|
|
Pretty annoying to keep typing `first` and `second` (especially if you have nested pairs ...)
|
|
|
|
### Vectors
|
|
|
|
```cpp
|
|
typedef vector<int> vi;
|
|
|
|
#define sz(x) (int)x.size()
|
|
#define all(x) begin(x), end(x)
|
|
```
|
|
|
|
It's generally a good idea to convert a size to a signed integer before doing anything with it to avoid cases like the following.
|
|
|
|
```cpp
|
|
vi x;
|
|
cout << x.size()-1 << "\n"; // 18446744073709551615
|
|
cout << sz(x)-1 << "\n"; // -1
|
|
```
|
|
|
|
`all(v)` makes sorting part or all of a vector a bit shorter.
|
|
|
|
```cpp
|
|
vi v = {2,4,1,5,3};
|
|
sort(1+all(v)); // {2,1,3,4,5}
|
|
sort(all(v)); // {1,2,3,4,5}
|
|
```
|
|
|
|
### Constants
|
|
|
|
```cpp
|
|
const int MOD = 1e9+7; // 998244353;
|
|
const int MX = 2e5+5;
|
|
const ll INF = 1e18;
|
|
const ld PI = acos((ld)-1);
|
|
```
|
|
|
|
$10^9+7$ is a prime that appears quite frequently in programming contests. Interestingly, $(10^9+7-1)/2=5\cdot 10^8+3$ is also prime. On the other hand, $998244353-1$ is divisible by $2^{23}$, which is useful for [NTT](https://en.wikipedia.org/wiki/Discrete_Fourier_transform_(general)#Number-theoretic_transform).
|
|
|
|
Almost all USACO problems satisfy $N\le 2\cdot 10^5$, so that's what `MX` is for.
|
|
|
|
### Generating Random Numbers
|
|
|
|
```cpp
|
|
mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count());
|
|
```
|
|
|
|
See [neal's blog](https://codeforces.com/blog/entry/61587) about why `rand()` is bad. Use `rng()` instead.
|
|
|
|
### Template
|
|
|
|
```cpp
|
|
template<class T> bool ckmin(T& a, const T& b) {
|
|
return b < a ? a = b, 1 : 0; }
|
|
template<class T> bool ckmax(T& a, const T& b) {
|
|
return a < b ? a = b, 1 : 0; }
|
|
```
|
|
|
|
See [negCyc](https://github.com/bqi343/USACO/blob/master/Implementations/content/graphs%20(12)/Basics/NegativeCycle%20(7.3).h) for an example of usage.
|
|
|
|
### Lambda Expressions
|
|
|
|
<resources>
|
|
<resource source="GFG" url="lambda-expression-in-c" title = "Lambda Expressions in C++"> </resource>
|
|
</resources>
|
|
|
|
(describe more) |