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https://github.com/huixxi/algorithm-with-cplusplus

Bro Yu's private home algorithm cuisine. You must like it.:cookie:
https://github.com/huixxi/algorithm-with-cplusplus

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Bro Yu's private home algorithm cuisine. You must like it.:cookie:

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README 

        
# Learning Algorithm with Yu in C++.

Bro Yu's Private Home Algorithm Cuisine.



### A typical C++ code template: 

```c++

#include 

using namespace std;



int main() {

    ios_base::sync_with_stdio(0);  // to speed up `cin` `cout`.

    cin.tie(0);

    /* ... */

}

```



### Using the following command to compile the code:

```shell

g++ -std=c++11 -O2 -Wall test.cpp -o test

```   

then, `./test` to run your code.(explain: `-O2` optimizes the code, `-Wall` shows warnings about possible errors)   



### Some tricks used in programming:  

* the newline `"\n"` works faster than `endl`, because `endl` always causes a flush operation.



### Input and Output

In most contests, standard streams are used for reading input and writing output.   

```c++

int a, b;

string x;

cin >> a >> b >> x;

```

```c++

int a = 123, b = 456;

string x = "input";

cout << a << b << x << "\n";

```

Besides `cin`、`cout`, we can also use `scanf` for input, `printf` for output.  

```c

int a, b;

scanf("%d %d", &a, &b);

```

```c

int a = 123, b = 456;

printf("%d %d\n", a, b);

```

For string containing spaces, we use `getline`:

```c++

string x;

getline(cin, x);

```

For the amount of data is unknown, the following loop is useful:

```c++

// loop reads elements from the input until there is no more data available.

while(cin >> x) {

    /* ... */

}

```

In some contest systems, files are used for input and output:

```c++

freopen("input.txt", "r", stdin);

freopen("output.txt", "w", stdout);

```



### Working with numbers

**Integers**(`long long` is usually enough)   

* `int`: `-2^31...2^31 - 1` or about `-2*10^9...2*10^9`

* `long long`: `-2^63...2^63 - 1` or about `-9*10^18...9*10^18`

* `__int128_t`: `-2^127...2^127 - 1` or about `-10^38...10^38`(may not available for all contest systems)



**Modular arithmetic**

```

(a + b) mod m = (a mod m + b mod m) mod m

(a − b) mod m = (a mod m − b mod m) mod m

(a · b) mod m = (a mod m · b mod m) mod m

```

make sure there are no negative remainders:

```

if (x < 0) x += m;

```



**Floating point numbers**  

The usual floating point types in competitive programming are the 64-bit `double` and, as an extension in the g++ compiler, the 80-bit `long double`. In most cases, `double` is enough, but `long double` is more accurate.   



An easy way to output the answer that required precision is to use the `printf` function and give the number of decimal places in the formatting string.

```c++

printf("%.9f\n", x);

```

Compare two float point number(to eliminate the round error):

```c++

if(abs(a - b) < 1e-9) {

    /* a and b are equal */

}

```



### Shortening code

**Type names**  

```c++

typedef long long ll;

typedef vector vi;

typedef pair pi;

```



**Macros**  

```c++

#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 SQ(a) (a)*(a)



// now

for(int i = 1; i < n; ++i) {

    search(i);

}

// become 

REP(i, 1, n) {

    search(i);

}

```



### Recommended books for coding competition & tech-interview

1. [Competitive Programmer’s Handbook(Free PDF)](https://cses.fi/book/book.pdf) :star:

2. [Cracking the Coding Interview 6th Edition: 189 Programming Questions and Solutions](http://ahmed-badawy.com/blog/wp-content/uploads/2018/10/Cracking-the-Coding-Interview-6th-Edition-189-Programming-Questions-and-Solutions.pdf)