MohammadParsaElahimanesh's blog

By MohammadParsaElahimanesh, 12 months ago, In English

Introduction

Radix sort is a sorting algorithm that sorts elements by grouping them based on their digits. It is a non-comparative sorting algorithm that is faster than many other sorting algorithms, including the default std::sort function in C++. In this blog post, we will explore how radix sort works and how to implement it in C++.

How Radix Sort Works

In radix sort, we sort elements based on their digits, starting from the least significant digit to the most significant digit. We group the elements based on each digit and sort them accordingly. This process is repeated for each digit until all digits have been considered. The result is a sorted list of elements.

Implementing Radix Sort in C++

Here's an implementation of radix sort in C++:

In this implementation, we first check if the input values are negative. If they are, we convert them to positive values, sort them, and then convert them back to negative values. We then loop through blocks of digits, starting from the least block, and sort the elements based on that block. We use a counting sort algorithm to sort the elements based on each block.

Performance Benchmarks

To compare the performance of radix sort with other sorting algorithms, we ran a benchmark test on several arrays of integers. Here are the results:

Array Size Data Type Radix Sort Time (ms) std::sort Time (ms)
1000 64-bit integers 0.503 0.098
1,000,000 64-bit integers 84.32 177.304
100,000,000 64-bit integers 8119.51 21297.8
1000 32-bit integers 0.296 0.088
1,000,000 32-bit integers 38.482 170.115
100,000,000 32-bit integers 4418.55 20673.5
1000 integers in range [0, 1e6) 0.159 0.098
1,000,000 integers in range [0, 1e6) 17.277 168.051
100,000,000 integers in range [0, 1e6) 2098 17265.4

As you can see, radix sort is faster than the default std::sort function in C++ for most of the test cases.

Conclusion

Radix sort is a powerful sorting algorithm that can be used to sort elements faster than many other sorting algorithms. In this blog post, we explored how radix sort works and how to implement it in C++. We also compared the performance of radix sort with other sorting algorithms and found that it is faster than the default std::sort function in C++ for most test cases. I hope this blog post has been helpful to you!

You can find the source code and every things on https://github.com/Mohammad-Parsa-Elahimanesh/Radix-sort-Cpp.

If you have any opinion or criticism or if the code can be improved in terms of beauty or functionality, I would be very grateful to say it in the comments.

at end thanks Bing Ai to help me write this blog.

I hope to be useful for you!

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By MohammadParsaElahimanesh, 2 years ago, In English

Hi Codeforces,

I've tried my best to make a different editorial, I wish you enjoy it ...

1746A - Maxmina

problem author: MohammadParsaElahimanesh, AmirrzwM

step by step solution
solution

1746B - Rebellion

problem author: MohammadParsaElahimanesh

step by step solution
solution

1746C - Permutation Operations

problem author: napstablook

step by step solution
solution

1746D - Paths on the Tree

problem author: AquaMoon, Cirno_9baka, mejiamejia, ChthollyNotaSeniorious, SSerxhs, TomiokapEace

single step solution
solution

1746E1 - Joking (Easy Version)

problem author: MohammadParsaElahimanesh

step by step solution
solution

1746E2 - Joking (Hard Version)

problem author: MohammadParsaElahimanesh, AmirrzwM

step by step solution
solution

1746F - Kazaee

problem author: MohammadParsaElahimanesh

step by step solution
solution

1746G - Olympiad Training

problem idea: SirShokoladina

problem development: SomethingNew, pakhomovee, SirShokoladina

single step solution
solution

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By MohammadParsaElahimanesh, history, 3 years ago, In English

Hello,

we have array A[n][n] and q queries. each time we get l r x means we should assign A[i][j] = x (l <= i,j <= r)

at end we want to know sum of elements in A, initially A[i][j] = 0

n <= 200'000

q <= 200'000

How we can solve this problem or what is the best time complexity we can reach?

thanks in advance

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By MohammadParsaElahimanesh, history, 3 years ago, In English

Hello, please fix output of test 26 in problem 1553F MikeMirzayanov

formally in this problem we should print n numbers (2 <= n <= 200'000)

but when we do such thing on test 26, occurs this error:(n = 199974 on test 26)

[wrong answer Output contains longer sequence [length = 199974], but answer contains 0 elements]

123563135 wrong answer on test 26

123564261 accepted when i ignore test 26(or n == 199974)

I'm sorry, actually I wasn't sure about where I should report this bug.

UPD : bug fixed and all wrong submissions(for this issue) rejudged.

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By MohammadParsaElahimanesh, history, 4 years ago, In English

Hello, Can we find for example each red node (in picture blow) in O(1)?

I try hard to find a way such as binary operations to get my ans. but i can't :(

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By MohammadParsaElahimanesh, history, 4 years ago, In English

Hello, many times you need to calculate lg2(n) and usually you need just to calculate floor of that. may these functions help you.

/// there are in O(1) and they work for int and long long numbers that is greater than 0
int lg2(const int &x){return 31 - __builtin_clz(x);}
long long int lg2(const long long int &x){return 63 - __builtin_clzll(x);}

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By MohammadParsaElahimanesh, history, 4 years ago, In English

In the name of Allah

--------------------

Hello my friends ! I have a prize for you, Actually I always have a problem with KMP. So I try to use hash string instead. I think it wood be great if we have a struct like hash and can easily work with it. So I make it ! here I implemented hash struct with C++ & you can have fun with it.

#include <bits/stdc++.h>

using namespace std;

template <typename X, typename Y, typename Z>
long long int Pow(const X &a, const Y &b, const Z &mod) /// # O(log(b))
{
    if(b == 0) return 1LL;
    long long int x = Pow(a,b/2,mod);
    return b%2 == 0? x*x%mod : (long long int)a * (x * x % mod) % mod;
}

bool ready = false;
const long long int MAX_Hash = 1e6 + 5;
const long long int mod1 = 1e9 + 7;
const long long int mod2 = 1e9 + 9;
const long long int C = 257LL;
long long int C1[MAX_Hash];
long long int C2[MAX_Hash];
long long int pow1[MAX_Hash];
long long int pow2[MAX_Hash];

void fill_C()
{
    C1[0] = C2[0] = 1LL;
    for(int i = 1; i < MAX_Hash; i++)
    {
        C1[i] = (C1[i-1] * C) % mod1;
        C2[i] = (C2[i-1] * C) % mod2;
    }
}

void fill_pow()
{
    pow1[0] = pow2[0] = 1LL;
    pow1[1] = Pow(C,mod1-2,mod1);
    pow2[1] = Pow(C,mod2-2,mod2);
    for(int i = 2; i < MAX_Hash; i++)
    {
        pow1[i] = pow1[i-1] * pow1[1] % mod1;
        pow2[i] = pow2[i-1] * pow2[1] % mod2;
    }
}

void GetReady()
{
    ready = true;
    fill_C();
    fill_pow();
}

struct Hash
{
    long long int val1 = 0, val2 = 0, S = 0;

    Hash() /// # O(1)
    {
        if(!ready)GetReady();
    }

    Hash(const char &x) /// # O(1)
    {
        Hash();
        push_back(x);
    }

    Hash(char *s, const char *e) /// # O(Len)
    {
        Hash();
        push_back(s,e);
    }

    Hash(const string &s) /// # O(len)
    {
        Hash();
        push_back(s);
    }

    Hash(const Hash &A) /// # O(1)
    {
        Hash();
        push_back(A);
    }

    void clear() /// # O(1)
    {
        S = val1 = val2 = 0LL;
    }

    void push_back(const char &x) /// # O(1)
    {
        S++;
        val1 *= C1[1];
        val1 += (long long int)x;
        val1 %= mod1;
        val2 *= C2[1];
        val2 += (long long int)x;
        val2 %= mod2;
    }

    void push_back(const string &s) /// # O(len)
    {
        for(auto u: s)
            push_back(u);
    }

    void push_back(char *s, const char *e) /// # O(len)
    {
        while(s != e)
        {
            push_back(*s);
            s++;
        }
    }

    void push_back(const Hash &A) /// # O(1)
    {
        val1 *= C1[A.S];
        val1 += A.val1;
        val1 %= mod1;
        val2 *= C2[A.S];
        val2 += A.val2;
        val2 %= mod2;
        S += A.S;
    }

    void push_front(const char &x) /// # O(1)
    {
        val1 += (long long int)x * C1[S];
        val1 %= mod1;
        val2 += (long long int)x * C2[S];
        val2 %= mod2;
        S++;
    }

    void push_front(const string &s) /// # O(len)
    {
        for(int i = s.size()-1; i >= 0; i--)
            push_front(s[i]);
    }

    void push_front(const char *s, char *e) /// # O(len)
    {
    if(e == s)return;
        do
        {
            e--;
            push_back(*e);
        }while(s != e);
    }

    void push_front(const Hash &A) /// # O(1)
    {
        val1 += A.val1 * C1[S];
        val1 %= mod1;
        val2 += A.val2 * C2[S];
        val2 %= mod2;
        S += A.S;
    }

    void operator+=(const Hash &A) /// # O(1)
    {
        push_back(A);
    }

    void operator+=(const char &x) /// # O(1)
    {
        push_back(x);
    }

    void operator+=(const string &s) /// # O(len)
    {
        push_back(s);
    }

    void pop_back(const char &x) /// # O(1)
    {
        S--;
        val1 -= (long long int)x;
        val1 *= pow1[1];
        val1 = ((val1%mod1)+mod1)%mod1;
        val2 -= (long long int)x;
        val2 *= pow2[1];
        val2 = ((val2%mod2)+mod2)%mod2;
    }

    void pop_back(const string &s) /// # O(len)
    {
        for(int i = s.size()-1; i >= 0; i--)
            pop_back(s[i]);
    }

    void pop_back(const char *s, char *e) /// # O(len)
    {
        if(e == s)return;
        do
        {
            e--;
            pop_back(*e);
        }while(s != e);
    }

    void pop_back(const Hash &A) /// # O(1)
    {
        S -= A.S;
        val1 -= A.val1;
        val1 *= pow1[A.S];
        val1 = ((val1%mod1)+mod1)%mod1;
        val2 -= A.val2;
        val2 *= pow2[A.S];
        val2 = ((val2%mod2)+mod2)%mod2;
    }

    void pop_front(const char &x) /// # O(1)
    {
        S--;
        val1 -= (long long int)x * C1[S];
        val1 = ((val1%mod1)+mod1)%mod1;
        val2 -= (long long int)x * C2[S];
        val2 = ((val2%mod2)+mod2)%mod2;
    }

    void pop_front(const string &s) /// # O(len)
    {
        for(auto u: s)
            pop_front(u);
    }

    void pop_front(char *s, const char *e) /// # O(len)
    {
        while(s!=e)
        {
            pop_front(*s);
            s++;
        }
    }

    void pop_front(const Hash &A) /// # O(1)
    {
        S -= A.S;
        val1 -= A.val1 * C1[S];
        val1 = (val1%mod1+mod1)%mod1;
        val2 -= A.val2 * C2[S];
        val2 = (val2%mod2+mod2)%mod2;
    }

    void operator-=(const Hash &A) /// # O(1)
    {
        pop_back(A);
    }

    void operator-=(const char &x) /// # O(1)
    {
        pop_back(x);
    }

    void operator-=(const string &s) /// # O(len)
    {
        pop_back(s);
    }

    void operator=(const char &s) /// # O(1)
    {
        val1 = (long long int)s;
        val2 = (long long int)s;
        S = 1LL;
    }

    void operator=(const string &s) /// # O(len)
    {
        clear();
        push_back(s);
    }

    void operator=(const Hash &A) /// # O(1)
    {
        val1 = A.val1;
        val2 = A.val2;
        S = A.S;
    }

    bool operator==(const Hash &A) const /// # O(1)
    {
        return (val1 == A.val1 && val2 == A.val2 && S == A.S);
    }

    bool operator==(const string &s) const /// # O(len)
    {
        Hash A(s);
        return (val1 == A.val1 && val2 == A.val2 && S == A.S);
    }

    bool operator==(const char &x) const /// # O(1)
    {
        return (val1 == (long long int)x && val2 == (long long int)x && S == 1);
    }

    bool empty() /// # O(1)
    {
        return (S == 0);
    }

    long long int size() /// # O(1)
    {
        return S;
    }
}EMPTY, PLUS, MINUS;

template <typename T>
Hash operator+(const Hash &A, const T &B)
{
    PLUS = A;
    PLUS += B;
    return PLUS;
}

template <typename T>
Hash operator-(const Hash &A, const T &B)
{
    MINUS = A;
    MINUS -= B;
    return MINUS;
}
int main()
{

    return 0;
}


you can push_back, pop_back, push_front, pop_front a char*, string ,a char and also a hash to your hash and many other work. notice mainly when you want to use a string or a char* program handle on O(length) but when you use hash or a char it will be O(1). and also for the first time you want to hash some thing program does Preprocessing in O(MAX_Hash) where MAX_Hash is max length of a string you want to hash it, you can easily set it. its default is 1e6 + 5.

For the theory part you can visit : https://cp-algorithms.com/string/string-hashing.html

about variable I use: S is length of hashed string, val1 is hash of string in mod mod1, val2 is hash of string in mod mod2. note : there is no Anti-hash yet that can hack you with this hash function.

Now I want to introduce functions one by one in examples:

    char t[20] = "Hash Struct . . .";
    string s = "OK!";
    Hash A; /// simple
    Hash B("Hello codeforces !"); /// give a string
    Hash C(t,t+17); /// give a char* with two pointers
    Hash D(B); /// give an other Hash

    B.clear(); /// now B is completely empty

    D.push_back('@'); /// -@- will added to end of D
    B.push_back(s); /// string s will added to end of B
    B.push_back(t,t+4); /// -Hash- (t,t+4) will added to end of B
    C.push_back(A); /// A will added to C but A was empty and has no effect

    D.push_front('_'); /// -_ will added to front of D
    B.push_front("String B is :"); /// -String B is :- will added to front of B
    A.push_front(t+5,t+12); /// -Struct - (t+5,t+12) will added to front of A
    C.push_front(A); /// A will added to front of C

    B += D; /// D will added to end of B
    A += '%'; /// -%- will added to end of A
    C += "I am C !"; /// -I am C !- will added to end of C

    /*
        notice pop_back and pop_front should give a real char, string, char* or a Hash
        for example A is "Struct" now and we can:
    */
    A.pop_back('t'); /// -Struct- -> -Struc-
    A.pop_back("uc"); /// -Struc- -> -Str-
    A.pop_back(t+7,t+8); /// -Str- -> -St-
    A.pop_back(A); /// It's unusual way to clear a Hash !

    /// B's front is -String B is :-
    B.pop_front("String"); /// -String B is :- -> - B is :-
    B.pop_front(' '); /// - B is :- -> -B is :-
    B.pop_front(t+4,t+4); /// nothing
    B.pop_front(B); /// It's unusual way to clear a Hash !

    /// -= is like pop_back so now C has -I am C !- at end
    C -= '!'; /// -I am C !- -> -I am C -
    C -= " C "; /// -I am C - -> -I am-
    C -= C; /// C now is empty but if for example Hash E = " am", you can write C -= E => -I am- -> -I-

    D = '*'; /// now D is just -*-
    A = "ABCD"; /// now A is just -ABCD-
    B = A; /// now B is just like A means -ABCD- here

    A == B; /// return true if A is_equal to B else false
    D == "ABDE"; /// return true if A is_equal to -ABDE- else false
    D == '*'; /// return true if D = -*- else false

    C.empty(); /// return true if and just if length of C is 0
    C.size(); /// return length of C

    D = A + B - C; /// D will be A + B - C(it's different from A - C + B)

At last If you have a suggestion or want to know something or find a bug(you can't find bug but maybe) or else please and please tell me by writing comments.

Hope to enjoy it.

THE END . . .

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