Prefix of a given String that are divisible by K

Given a 0-indexed based string str of length n consisting of digits, and a positive integer K, the task is to find the prefixes of a String that are exactly Divisible by K. Store the prefix that is divisible by K, in a vector of String and print them. String word str consists of only digits from 0 to 9. 

Examples:  

Input: Str = "998244353", K = 3
Output:  Prefixes of a String that are Divisible by 3 : "9", "99", "998244", "9982443". 
Explanation: There are only 4 prefixes that are divisible by 3: "9", "99", "998244", and "9982443".  

Input: Str = "1010", K = 10
Output:  Prefixes of a String that are Divisible by 10 : "10", and "1010". 
Explanation: There are only 2 prefixes that are divisible by 10: "10", and "1010".

Approach: To solve the problem follow the below steps:

• Create an Ans String Vector to store prefixes of string.
• Create a NUM variable of type long long int and iterate the string and calculate the prefix value, num = num * 10 + (Str[i] - '0').
• Check if that NUM is divisible by K, push back the current prefix to a vector by converting it to the string,
  • if (num % (unsigned long long int)K == 0)
  • Ans.push_back(to_string(num)).
• Print the Ans string.

Below is the implementation of the above approach:   

// Program to print prefixes of string
// that are divisible by K
#include <bits/stdc++.h>
using namespace std;
void prefixes_strings(string STR, int K,
                      vector<string>& Ans)
{
    long long int num = 0;
    for (int i = 0; i < STR.length(); i++) {
        num = num * 10 + (STR[i] - '0');
        if (num % (unsigned long long int)K == 0)
            Ans.push_back(to_string(num));
    }
}

// Drivers code
int main()
{
    string STR = "998244353";
    int K = 3;
    vector<string> Ans;

    // Function Call
    prefixes_strings(STR, K, Ans);
    cout << "prefixes of a string that are divisible by "
         << K << ":";
    for (int i = 0; i < Ans.size(); i++) {
        cout << "'" << Ans[i] << "'"
             << " ";
    }
    return 0;
}

// Java Program to print prefixes of string
// that are divisible by K
import java.util.*;

public class GFG
{

  // A function to find all prefixes of a 
  // string that are divisible by K
  public static void prefixes_strings(String STR, int K,
                                      ArrayList<String> Ans) 
  {

    // A variable to store the current number
    long num = 0;

    // Iterate through each character in the string
    for (int i = 0; i < STR.length(); i++) {
      // Convert the current substring to a number
      num = num * 10 + (STR.charAt(i) - '0');

      // If the number is divisible by K, add it to the answer vector
      if (num % K == 0)
        Ans.add(Long.toString(num));
    }
  }

  // Drivers code
  public static void main(String[] args) {
    // Input string and the value of K
    String STR = "998244353";
    int K = 3;
    ArrayList<String> Ans = new ArrayList<>();

    // Function Call
    prefixes_strings(STR, K, Ans);
    System.out.print("prefixes of a string that are divisible by " + K + ": ");
    for (int i = 0; i < Ans.size(); i++) {
      System.out.print("'" + Ans.get(i) + "' ");
    }
  }
}

def prefixes_strings(STR, K, Ans):
    num = 0
    for i in range(len(STR)):
        num = num * 10 + int(STR[i])
        if num % K == 0:
            Ans.append(str(num))


STR = "998244353"
K = 3
Ans = []

# Function Call
prefixes_strings(STR, K, Ans)
print("prefixes of a string that are divisible by", K, ":", end=" ")
for i in range(len(Ans)):
    print("'" + Ans[i] + "'", end=" ")

// C# Program to print prefixes of string
// that are divisible by K

using System;
using System.Collections.Generic;

public class GFG {
      // Drivers code
    public static void Main()
    {
          // Input string and the value of K
        string str = "998244353";
        int k = 3;
        List<string> ans = new List<string>();
    
          // Function call
        PrefixesStrings(str, k, ans);
        Console.Write($"Prefixes of a string that are divisible by {k}: ");
        foreach (string s in ans)
        {
            Console.Write($"'{s}' ");
        }
    }

      // A function to find all prefixes of a 
      // string that are divisible by K
    public static void PrefixesStrings(string str, int k, List<string> ans)
    {
          // A variable to store the current number
        long num = 0;
      
          // Iterate through each character in the string
        for (int i = 0; i < str.Length; i++)
        {
              // Convert the current substring to a number
            num = num * 10 + (str[i] - '0');
          
              // If the number is divisible by K, add it to the answer vector
            if ((ulong)num % (ulong)k == 0)
            {
                ans.Add(num.ToString());
            }
        }
    }
}

function prefixes_strings(STR, K, Ans) {
  let num = 0;
  for (let i = 0; i < STR.length; i++) {
    num = num * 10 + (STR.charCodeAt(i) - "0".charCodeAt(0));
    if (num % K === 0) {
      Ans.push(num.toString());
    }
  }
}

// Drivers code
let STR = "998244353";
let K = 3;
let Ans = [];

// Function Call
prefixes_strings(STR, K, Ans);
console.log(`prefixes of a string that are divisible by ${K}:`);
for (let i = 0; i < Ans.length; i++) {
  console.log(`'${Ans[i]}' `);
}

prefixes of a string that are divisible by K:'9' '99' '998244' '9982443' 

Time Complexity: O(N) where N is the length of the string
Auxiliary Space: O(1) 

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Article Tags :

• Strings
• DSA

Practice Tags :

• Strings