Given a number as a string, find the number of contiguous subsequences which recursively add up to 9

Given a number as a string, write a function to find the number of substrings (or contiguous subsequences) of the given string which recursively add up to 9.

For example digits of 729 recursively add to 9,
7 + 2 + 9 = 18
Recur for 18
1 + 8 = 9

Examples:

 
Input: 4189
Output: 3
There are three substrings which recursively add to 9.
The substrings are 18, 9 and 189.

Input: 999
Output: 6
There are 6 substrings which recursively add to 9.
9, 99, 999, 9, 99, 9

All digits of a number recursively add up to 9, if only if the number is multiple of 9. We basically need to check for s%9 for all substrings s. One trick used in below program is to do modular arithmetic to avoid overflow for big strings.

Following is a simple implementation based on this approach. The implementation assumes that there are no leading 0’s in input number.

C++

// C++ program to count substrings with recursive sum equal to 9 
#include <iostream> 
#include <cstring> 
using namespace std; 
  
int count9s(char number[]) 
{ 
    int count = 0; // To store result 
    int n = strlen(number); 
  
    // Consider every character as beginning of substring 
    for (int i = 0; i < n; i++) 
    { 
        int sum = number[i] - '0';  //sum of digits in current substring 
  
        if (number[i] == '9') count++; 
  
        // One by one choose every character as an ending character 
        for (int j = i+1; j < n; j++) 
        { 
            // Add current digit to sum, if sum becomes multiple of 5 
            // then increment count. Let us do modular arithmetic to 
            // avoid overflow for big strings 
            sum = (sum + number[j] - '0')%9; 
  
            if (sum == 0) 
               count++; 
        } 
    } 
    return count; 
} 
  
// driver program to test above function 
int main() 
{ 
    cout << count9s("4189") << endl; 
    cout << count9s("1809"); 
    return 0; 
} 

Java

// Java program to count 
// substrings with  
// recursive sum equal to 9 
import java.io.*; 
  
class GFG 
{ 
static int count9s(String number) 
{ 
    // To store result 
    int count = 0;  
    int n = number.length(); 
  
    // Consider every character  
    // as beginning of substring 
    for (int i = 0; i < n; i++) 
    { 
        // sum of digits in 
        // current substring 
        int sum = number.charAt(i) - '0';  
  
        if (number.charAt(i) == '9')  
            count++; 
  
        // One by one choose  
        // every character as  
        // an ending character 
        for (int j = i + 1; 
                 j < n; j++) 
        { 
            // Add current digit to  
            // sum, if sum becomes  
            // multiple of 5 then  
            // increment count. Let 
            // us do modular arithmetic  
            // to avoid overflow for  
            // big strings 
            sum = (sum + 
                   number.charAt(j) -  
                            '0') % 9; 
  
            if (sum == 0) 
            count++; 
        } 
    } 
    return count; 
} 
  
// Driver Code 
public static void main (String[] args)  
{ 
    System.out.println(count9s("4189")); 
    System.out.println(count9s("1809")); 
} 
} 
  
// This code is contributed  
// by anuj_67. 

Python 3

# Python 3 program to count substrings 
# with recursive sum equal to 9 
  
def count9s(number): 
  
    count = 0 # To store result 
    n = len(number) 
  
    # Consider every character as  
    # beginning of substring 
    for i in range(n): 
          
        # sum of digits in current substring 
        sum = ord(number[i]) - ord('0')      
  
        if (number[i] == '9'): 
            count += 1
  
        # One by one choose every character  
        # as an ending character 
        for j in range(i + 1, n): 
          
            # Add current digit to sum, if  
            # sum becomes multiple of 5 then 
            # increment count. Let us do  
            # modular arithmetic to avoid  
            # overflow for big strings 
            sum = (sum + ord(number[j]) - 
                         ord('0')) % 9
  
            if (sum == 0): 
                count += 1
    return count 
  
# Driver Code 
if __name__ == "__main__": 
      
    print(count9s("4189")) 
    print(count9s("1809")) 
  
# This code is contributed by ita_c 

C#

// C# program to count 
// substrings with  
// recursive sum equal to 9 
using System; 
class GFG 
{ 
static int count9s(String number) 
{ 
    // To store result 
    int count = 0;  
    int n = number.Length; 
  
    // Consider every character  
    // as beginning of substring 
    for (int i = 0; i < n; i++) 
    { 
        // sum of digits in 
        // current substring 
        int sum = number[i] - '0';  
  
        if (number[i] == '9')  
            count++; 
  
        // One by one choose  
        // every character as  
        // an ending character 
        for (int j = i + 1; 
                 j < n; j++) 
        { 
            // Add current digit to  
            // sum, if sum becomes  
            // multiple of 5 then  
            // increment count. Let 
            // us do modular arithmetic  
            // to avoid overflow for  
            // big strings 
            sum = (sum + number[j] -  
                           '0') % 9; 
  
            if (sum == 0) 
            count++; 
        } 
    } 
    return count; 
} 
  
// Driver Code 
public static void Main ()  
{ 
    Console.WriteLine(count9s("4189")); 
    Console.WriteLine(count9s("1809")); 
} 
} 
  
// This code is contributed  
// by anuj_67. 

PHP

<?php 
// PHP program to count substrings 
// with recursive sum equal to 9 
  
function count9s($number) 
{ 
    // To store result 
    $count = 0;  
    $n = strlen($number); 
  
    // Consider every character as 
    // beginning of substring 
    for ($i = 0; $i < $n; $i++) 
    { 
        //sum of digits in  
        // current substring 
        $sum = $number[$i] - '0';  
  
        if ($number[$i] == '9') $count++; 
  
        // One by one choose every character 
        // as an ending character 
        for ($j = $i + 1; $j < $n; $j++) 
        { 
              
            // Add current digit to sum,  
            // if sum becomes multiple of 5 
            // then increment count. Let us  
            // do modular arithmetic to 
            // avoid overflow for big strings 
            $sum = ($sum + $number[$j] - '0') % 9; 
  
            if ($sum == 0) 
            $count++; 
        } 
    } 
    return $count; 
} 
  
    // Driver Code 
    echo count9s("4189"),"\n"; 
    echo count9s("1809"); 
      
// This code is contributed by ajit 
?> 

Output:

3
5

Time complexity of the above program is O(n²). Please let me know if there is a better solution.

Given a number as a string, find the number of contiguous subsequences which recursively add up to 9 | Set 2

This article is contributed by Abhishek. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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My Personal Notes

C++

Java

Python 3

C#

PHP

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