如何设计一个很小的URL或URL缩短器？

如何设计一个采用大网址(例如“ https://www.geeksforgeeks.org/count-sum-of-digits-in-numbers-from-1-to-n/”)的系统并将其转换为短6个字符网址。假定URL已存储在数据库中，并且每个URL都有一个关联的整数ID。

需要注意的重要一件事是，长网址也应该可以从短网址中唯一地识别出来。所以我们需要一个双射函数

我们强烈建议您单击此处并进行实践，然后再继续解决方案。

一种简单的解决方案是散列。使用哈希函数将长字符串转换为短字符串。在散列中，这可能是冲突(2个长URL映射到相同的短URL)，我们需要为每个长URL唯一的短URL，以便我们可以访问长URL。

更好的方法是使用存储在数据库中的整数ID和整数转换成，是长最多为6个字符。这个问题基本上可以看作是一个基本的转换问题，其中我们有一个10位数字的输入数字，并且我们希望将其转换为6个字符长的字符串。

以下是有关URL中可能的字符的一项重要观察。

URL字符可以是以下之一
1)小写字母[‘a’到’z’]，共26个字符
2)大写字母[‘A’至’Z’]，共26个字符
3)一个数字[‘0’到’9’]，共10个字符

一共有26 + 26 + 10 = 62个可能的字符。

因此，任务是将十进制数转换为以62为基数的数字。

要获取原始的长URL，我们需要在数据库中获取URL ID。可以使用以62为底的十进制转换来获取ID。

C++

// C++ program to generate short url from integer id and
// integer id back from short url.
#include
#include
#include
using namespace std;
  
// Function to generate a short url from integer ID
string idToShortURL(long int n)
{
    // Map to store 62 possible characters
    char map[] = "abcdefghijklmnopqrstuvwxyzABCDEF"
                 "GHIJKLMNOPQRSTUVWXYZ0123456789";
  
    string shorturl;
  
    // Convert given integer id to a base 62 number
    while (n)
    {
        // use above map to store actual character
        // in short url
        shorturl.push_back(map[n%62]);
        n = n/62;
    }
  
    // Reverse shortURL to complete base conversion
    reverse(shorturl.begin(), shorturl.end());
  
    return shorturl;
}
  
// Function to get integer ID back from a short url
long int shortURLtoID(string shortURL)
{
    long int id = 0; // initialize result
  
    // A simple base conversion logic
    for (int i=0; i < shortURL.length(); i++)
    {
        if ('a' <= shortURL[i] && shortURL[i] <= 'z')
          id = id*62 + shortURL[i] - 'a';
        if ('A' <= shortURL[i] && shortURL[i] <= 'Z')
          id = id*62 + shortURL[i] - 'A' + 26;
        if ('0' <= shortURL[i] && shortURL[i] <= '9')
          id = id*62 + shortURL[i] - '0' + 52;
    }
    return id;
}
  
// Driver program to test above function
int main()
{
    int n = 12345;
    string shorturl = idToShortURL(n);
    cout << "Generated short url is " << shorturl << endl;
    cout << "Id from url is " << shortURLtoID(shorturl);
    return 0;
}

Java

// Java program to generate short url from integer id and 
// integer id back from short url. 
import java.util.*;
import java.lang.*;
import java.io.*;
  
class GFG
{
    // Function to generate a short url from integer ID 
    static String idToShortURL(int n) 
    { 
        // Map to store 62 possible characters 
        char map[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".toCharArray(); 
      
        StringBuffer shorturl = new StringBuffer(); 
      
        // Convert given integer id to a base 62 number 
        while (n > 0) 
        { 
            // use above map to store actual character 
            // in short url 
            shorturl.append(map[n % 62]);
            n = n / 62; 
        } 
      
        // Reverse shortURL to complete base conversion 
        return shorturl.reverse().toString(); 
    } 
      
    // Function to get integer ID back from a short url 
    static int shortURLtoID(String shortURL) 
    { 
        int id = 0; // initialize result 
      
        // A simple base conversion logic 
        for (int i = 0; i < shortURL.length(); i++) 
        { 
            if ('a' <= shortURL.charAt(i) && 
                       shortURL.charAt(i) <= 'z') 
            id = id * 62 + shortURL.charAt(i) - 'a'; 
            if ('A' <= shortURL.charAt(i) && 
                       shortURL.charAt(i) <= 'Z') 
            id = id * 62 + shortURL.charAt(i) - 'A' + 26; 
            if ('0' <= shortURL.charAt(i) && 
                       shortURL.charAt(i) <= '9') 
            id = id * 62 + shortURL.charAt(i) - '0' + 52; 
        } 
        return id; 
    } 
      
    // Driver Code
    public static void main (String[] args) throws IOException
    {
        int n = 12345; 
        String shorturl = idToShortURL(n); 
        System.out.println("Generated short url is " + shorturl); 
        System.out.println("Id from url is " + 
                            shortURLtoID(shorturl)); 
    }
}
  
// This code is contributed by shubham96301

Python3

# Python3 code for above approach 
def idToShortURL(id):
    map = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
    shortURL = ""
      
    # for each digit find the base 62
    while(id > 0):
        shortURL += map[id % 62]
        id //= 62
  
    # reversing the shortURL
    return shortURL[len(shortURL): : -1]
  
def shortURLToId(shortURL):
    id = 0
    for i in shortURL:
        val_i = ord(i)
        if(val_i >= ord('a') and val_i <= ord('z')):
            id = id*62 + val_i - ord('a')
        elif(val_i >= ord('A') and val_i <= ord('Z')):
            id = id*62 + val_i - ord('Z') + 26
        else:
            id = id*62 + val_i - ord('0') + 52
    return id
  
if (__name__ == "__main__"):
    id = 12345
    shortURL = idToShortURL(id)
    print("Short URL from 12345 is : ", shortURL)
    print("ID from", shortURL, "is : ", shortURLToId(shortURL))

输出：

Generated short url is dnh
Id from url is 12345

优化：我们可以避免idToShortURL()中的反向步骤。为了确保返回相同的ID，我们还需要更改shortURLtoID()以从头开始而不是从头开始处理字符。