Given a string representing a number, we need to get the sum of all possible sub strings of this string.**Examples :**

Input : s = "6759" Output : 8421 sum = 6 + 7 + 5 + 9 + 67 + 75 + 59 + 675 + 759 + 6759 = 8421 Input : s = "16" Output : 23 sum = 1 + 6 + 16 = 23

We have discussed a solution in below post.

Sum of all substrings of a string representing a number | Set 1

The solution is based on a different approach which does not use any extra space.

This problem can be viewed as follows.

Let number be s = “6759”

1 10 100 1000 6 1 1 1 1 7 2 2 2 5 3 3 9 4

The above table indicates that, when all the substrings are converted further to the ones, tens, hundreds etc.. form, each index of the string will have some fixed occurrence. The 1st index will have 1 occurrence each of ones, tens etc..The 2nd will have 2, 3rd will have 3 and so on.

One more point is that the occurrence of the last element will only be restricted to ones. Last 2nd element will be restricted to ones and tens. last 3rd will be up to a hundred and so on.

From the above points lets find out the sum.

sum = 6*(1*1 + 1*10 + 1*100 + 1*1000) + 7*(2*1 + 2*10 + 2*100) + 5*(3*1 + 3*10) + 9*(4*1) = 6*1*(1111) + 7*2*(111) + 5*3*(11) + 9*4*(1) = 6666 + 1554 + 165 + 36 = 8421

Now, to handle the multiplication we will be having a multiplying factor which starts from 1. It’s clear from the example that the multiplying factor(in reverse) is 1, 11, 111, … and so on. So the multiplication will be based on three factors. number, its index, and a multiplying factor.

## C++

`// C++ program to print sum of all substring of` `// a number represented as a string` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Returns sum of all substring of num` `int` `sumOfSubstrings(string num)` `{` ` ` `long` `long` `int` `sum = 0; ` `// Initialize result` ` ` `// Here traversing the array in reverse` ` ` `// order.Initializing loop from last` ` ` `// element.` ` ` `// mf is multiplying factor.` ` ` `long` `long` `int` `mf = 1;` ` ` `for` `(` `int` `i=num.size()-1; i>=0; i--)` ` ` `{` ` ` `// Each time sum is added to its previous` ` ` `// sum. Multiplying the three factors as` ` ` `// explained above.` ` ` `// s[i]-'0' is done to convert char to int.` ` ` `sum += (num[i]-` `'0'` `)*(i+1)*mf;` ` ` `// Making new multiplying factor as` ` ` `// explained above.` ` ` `mf = mf*10 + 1;` ` ` `}` ` ` `return` `sum;` `}` `// Driver code to test above methods` `int` `main()` `{` ` ` `string num = ` `"6759"` `;` ` ` `cout << sumOfSubstrings(num) << endl;` ` ` `return` `0;` `}` |

## Java

`// Java program to print sum of all substring of` `// a number represented as a string` `import` `java.util.Arrays;` `public` `class` `GFG {` ` ` ` ` `// Returns sum of all substring of num` ` ` `public` `static` `long` `sumOfSubstrings(String num)` ` ` `{` ` ` `long` `sum = ` `0` `; ` `// Initialize result` ` ` ` ` `// Here traversing the array in reverse` ` ` `// order.Initializing loop from last` ` ` `// element.` ` ` `// mf is multiplying factor.` ` ` `long` `mf = ` `1` `;` ` ` `for` `(` `int` `i = num.length() - ` `1` `; i >= ` `0` `; i --)` ` ` `{` ` ` `// Each time sum is added to its previous` ` ` `// sum. Multiplying the three factors as` ` ` `// explained above.` ` ` `// s[i]-'0' is done to convert char to int.` ` ` `sum += (num.charAt(i) - ` `'0'` `) * (i + ` `1` `) * mf;` ` ` ` ` `// Making new multiplying factor as` ` ` `// explained above.` ` ` `mf = mf * ` `10` `+ ` `1` `;` ` ` `}` ` ` ` ` `return` `sum;` ` ` `}` ` ` ` ` ` ` `// Driver code to test above methods` ` ` `public` `static` `void` `main(String[] args)` ` ` `{` ` ` `String num = ` `"6759"` `;` ` ` ` ` `System.out.println(sumOfSubstrings(num));` ` ` ` ` `}` `}` `// This code is contributed by Arnav Kr. Mandal.` |

## Python3

`# Python3 program to print sum of all substring of` `# a number represented as a string` `# Returns sum of all substring of num` `def` `sumOfSubstrings(num):` ` ` `sum` `=` `0` `# Initialize result` ` ` `# Here traversing the array in reverse` ` ` `# order.Initializing loop from last` ` ` `# element.` ` ` `# mf is multiplying factor.` ` ` `mf ` `=` `1` ` ` `for` `i ` `in` `range` `(` `len` `(num) ` `-` `1` `, ` `-` `1` `, ` `-` `1` `):` ` ` `# Each time sum is added to its previous` ` ` `# sum. Multiplying the three factors as` ` ` `# explained above.` ` ` `# int(s[i]) is done to convert char to int.` ` ` `sum` `=` `sum` `+` `(` `int` `(num[i])) ` `*` `(i ` `+` `1` `) ` `*` `mf` ` ` `# Making new multiplying factor as` ` ` `# explained above.` ` ` `mf ` `=` `mf ` `*` `10` `+` `1` ` ` `return` `sum` `# Driver code to test above methods` `if` `__name__` `=` `=` `'__main__'` `:` ` ` `num ` `=` `"6759"` ` ` `print` `(sumOfSubstrings(num))` `# This code is contributed by` `# Sanjit_Prasad` |

## C#

`// C# program to print sum of all substring of` `// a number represented as a string` `using` `System;` ` ` `public` `class` `GFG {` ` ` ` ` `// Returns sum of all substring of num` ` ` `public` `static` `long` `sumOfSubstrings(` `string` `num)` ` ` `{` ` ` ` ` `long` `sum = 0; ` `// Initialize result` ` ` ` ` `// Here traversing the array in reverse` ` ` `// order.Initializing loop from last` ` ` `// element.` ` ` `// mf is multiplying factor.` ` ` `long` `mf = 1;` ` ` ` ` `for` `(` `int` `i = num.Length - 1; i >= 0; i --)` ` ` `{` ` ` ` ` `// Each time sum is added to its previous` ` ` `// sum. Multiplying the three factors as` ` ` `// explained above.` ` ` `// s[i]-'0' is done to convert char to int.` ` ` `sum += (num[i] - ` `'0'` `) * (i + 1) * mf;` ` ` ` ` `// Making new multiplying factor as` ` ` `// explained above.` ` ` `mf = mf * 10 + 1;` ` ` `}` ` ` ` ` `return` `sum;` ` ` `}` ` ` ` ` ` ` `// Driver code to test above methods` ` ` `public` `static` `void` `Main()` ` ` `{` ` ` `string` `num = ` `"6759"` `;` ` ` ` ` `Console.WriteLine(sumOfSubstrings(num));` ` ` ` ` `}` `}` `// This code is contributed by Sam007.` |

## PHP

`<?php` `// PHP program to print sum of` `// all substring of a number` `// represented as a string` `// Returns sum of all` `// substring of num` `function` `sumOfSubstrings(` `$num` `)` `{` ` ` `// Initialize result` ` ` `$sum` `= 0;` ` ` `// Here traversing the array` ` ` `// in reverse order.Initializing` ` ` `// loop from last element.` ` ` `// mf is multiplying factor.` ` ` `$mf` `= 1;` ` ` `for` `(` `$i` `= ` `strlen` `(` `$num` `) - 1; ` `$i` `>= 0; ` `$i` `--)` ` ` `{` ` ` `// Each time sum is added to` ` ` `// its previous sum. Multiplying` ` ` `// the three factors as explained above.` ` ` `// s[i]-'0' is done to convert char to int.` ` ` `$sum` `+= (` `$num` `[` `$i` `] - ` `'0'` `) * (` `$i` `+ 1) * ` `$mf` `;` ` ` `// Making new multiplying` ` ` `// factor as explained above.` ` ` `$mf` `= ` `$mf` `* 10 + 1;` ` ` `}` ` ` `return` `$sum` `;` `}` `// Driver Code` `$num` `= ` `"6759"` `;` `echo` `sumOfSubstrings(` `$num` `), ` `"\n"` `;` `// This code is contributed by m_kit` `?>` |

## Javascript

`<script>` ` ` `// Javascript program to print sum of all substring of` ` ` `// a number represented as a string` ` ` ` ` `// Returns sum of all substring of num` ` ` `function` `sumOfSubstrings(num)` ` ` `{` ` ` ` ` `let sum = 0; ` `// Initialize result` ` ` ` ` `// Here traversing the array in reverse` ` ` `// order.Initializing loop from last` ` ` `// element.` ` ` `// mf is multiplying factor.` ` ` `let mf = 1;` ` ` ` ` `for` `(let i = num.length - 1; i >= 0; i --)` ` ` `{` ` ` ` ` `// Each time sum is added to its previous` ` ` `// sum. Multiplying the three factors as` ` ` `// explained above.` ` ` `// s[i]-'0' is done to convert char to int.` ` ` `sum += (num[i].charCodeAt() - ` `'0'` `.charCodeAt()) * (i + 1) * mf;` ` ` ` ` `// Making new multiplying factor as` ` ` `// explained above.` ` ` `mf = mf * 10 + 1;` ` ` `}` ` ` ` ` `return` `sum;` ` ` `}` ` ` ` ` `let num = ` `"6759"` `; ` ` ` `document.write(sumOfSubstrings(num));` ` ` ` ` `// This code is contributed by rameshtravel07.` `</script>` |

**Output :**

8421

This article is contributed by **Jatin Goyal**. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the **DSA Self Paced Course** at a student-friendly price and become industry ready. To complete your preparation from learning a language to DS Algo and many more, please refer **Complete Interview Preparation Course****.**

In case you wish to attend live classes with industry experts, please refer **DSA Live Classes**