Concept and application of logarithm

1. Generates an array of random numbers of random length

#include <iostream>
#include <time.h> 
#include <cstdlib>
#include<vector>
using namespace std;
vector<int> get_random_arr(int maxlen, int maxnum)
{
    
	srand((unsigned)time(NULL));
	int L = rand() % maxlen;
	cout << "L=" << L << endl;
	vector<int> Arr(L, 0);
	for (int i = 0; i < Arr.size(); i++)
	{
    
		Arr[i] = (rand() % (maxnum+1)) - (rand() % (maxnum+1));//[0,max_num]-[0,max_num]
	}
	return Arr;
}
int main()
{
    
	int max_len = 10;
	int max_num = 10;

	vector<int> res = get_random_arr(max_len, max_num);
	cout << res.size() << endl;
	for (int i = 0; i < res.size(); i++)
	{
    
		cout << res[i] << " ";
	}
	return 0;
}

2. c++ Generate random numbers
   To generate random numbers within a specified range , You can use it first rand() The function produces a [0,RAND_MAX] Random numbers in the range , Then, after the transformation to the specified range .
   produce [a,b) The random number , have access to (rand() % (b-a))+a;
   produce [a,b] The random number , have access to (rand() % (b-a+1))+a;
   produce (a,b] The random number , have access to (rand() % (b-a))+a+1;
   General formula ：a+rand() % n;
   among ：a Is the starting position of the range ,n Is the range of integers
   produce [a,b] The random number , have access to a+(int)b*rand()/(RAND_MAX+1);
   produce [0,1] Floating point number , have access to rand()/double(RAND_MAX)

#include <iostream>
#include <cstdlib>
#include <time.h>
using namespace std;

int main()
{
    
       cout <<"RAND_MAX:"<< RAND_MAX << endl;
       srand((unsigned)time(NULL));
       for (int i = 0; i < 5; i++)
              cout << (rand()%2)<<" ";         // Generate [0,1] Random numbers in the range 
       cout << endl;
       for (int i = 0; i < 5; i++)
              cout << (rand() % 5 + 3) << " "; // Generate [3,7] Random numbers in the range 
       cout << endl;
}

3. Application of logarithm
   To make sure your code is completely correct , Not just on some use cases , You need a logarithm to judge ; Generate a random array , Then throw into the selection sort and bubble sort respectively , Compare the results , If the results correspond to different , Then two codes should be good, one , Or it's all wrong ;
   Set the number of comparisons , If say 50 Ten thousand times , Each time a random array is generated , Put it into two sorting algorithms , Compare the results returned by the two algorithms ; If the results of each comparison are equal , It shows that both algorithms are correct , If you return false, It depends on the correctness of the algorithm ; It can also correspond to the language algorithm api Compare ;

• code

#include <iostream>
#include <time.h> 
#include <cstdlib>
#include<vector>
using namespace std;
// Insertion sort , Ascending 
vector<int> get_insert(vector<int>& Arr)
{
    
	for (int i = 1; i < Arr.size(); i++)
	{
    
		for (int j = i - 1; j >= 0 && Arr[j] > Arr[i]; j--)
		{
    
			swap(Arr[j], Arr[i]);
		}
	}
	return Arr;
}

// Selection sort 
vector<int> get_sort(vector<int>& Arr)
{
    
	for (int i = 0; i < Arr.size(); i++)
	{
    
		int minidx = i;
		for (int j = i + 1; j < Arr.size(); j++)
		{
    
			minidx = (Arr[minidx] < Arr[j] ? minidx : j);
		}
		swap(Arr[i], Arr[minidx]);
	}
	return Arr;
}

vector<int> get_random_arr(int maxlen, int maxnum)
{
    
	srand((unsigned)time(NULL));
	int L = rand() % maxlen;
	vector<int> Arr(L, 0);
	for (int i = 0; i < Arr.size(); i++)
	{
    
		Arr[i] = (rand() % (maxnum+1)) - (rand() % (maxnum+1));//[0,max_num]-[0,max_num]
	}
	return Arr;
}

bool compare(vector<int>& A, vector<int>& B)
{
    
	if (A != B)
		return false;
	return true;
}

int main()
{
    
	int max_len = 100;
	int max_num = 100;
	int test_num = 100;
	int res_flag = true;
	for (int i = 0;i < test_num ; i++)
	{
    
		vector<int> rand_arr1 = get_random_arr(max_len, max_num);
		vector<int> rand_arr2 = rand_arr1;
		vector<int> res1 = get_insert(rand_arr1);
		vector<int> res2 = get_insert(rand_arr2);
		if (!compare(res1, res2))
		{
    
			cout << "fasle" << endl;
			break;
		}
	}
	cout << "success" << endl;
	return 0;
}