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Sum of all possible expressions of a numeric string possible by inserting addition operators

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  • Difficulty Level : Easy
  • Last Updated : 27 Dec, 2022
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Given a numeric string str of length N, the task is to find the sum of all possible expressions by inserting the ‘+’ operator between the characters of the string any number of times.

Examples:

Input: str = “125” Output: 176 Explanation: Inserting “+” after 1st index modifies str to “1+25” and value = 26 Inserting “+” after 2nd index modifies str to “12+5” and value = 17 Inserting “+” after both 1st and 2nd index modifies str to “1+2+5” and value = 8 Therefore, the total sum of all possible expression is 125 + 26 + 17 + 8 = 176

Input: str = “9999999999”
Output: 12656242944

Approach: The idea is to insert the ‘+’ operator at all possible index of the string in all possible ways and calculate the sum. Finally, print the total sum obtained. Follow the steps below to solve the problem:

  • Initialize a variable say, sumOfExp to store the sum of all possible expression by inserting the ‘+’ operator at all possible indices of the string.
  • Generate all possible subset of indices of the string iteratively. For every subset of indices inserts the ‘+’ operator at elements of the subset and increment sumOfExp by the sum of the current expression.
  • Finally, print the value of sumOfExp.

Below is the implementation of the above approach:

C++




// C++ program to implement
// the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to find sum of all expressions by
// inserting '+' operator at all possible indices
void findSumOfExpressions(string S, int N)
{
  // Stores sum of all expressions by inserting
  // '+' operator at all possible indices
  unsigned long long sumOfExp = 0;
 
  // Generate all possible subset
  // of indices iteratively
  for (int i = 0; i < pow(2, N - 1); i++) {
    // Stores sum of
    // current expressions
    unsigned long long ans_sub = 0;
 
    // Stores numbers of
    // current expressions
    string subst = string(1, S.at(0));
 
    // Traverse the string at insert + at
    // current subset of indices
    for (int j = 0; j < N - 1; j++) {
      // If current index exists
      // in the current subset
      if (((i >> j) & 1) == 1) {
        // Update ans_sub
        ans_sub += stoull(subst);
 
        // Update subset
        subst = string(1, S.at(j + 1));
      }
      else
        // Update subset
        subst += S.at(j + 1);
 
      // + can't be inserted after
      // the last index
      if (j == N - 2)
        ans_sub += stoull(subst);
    }
 
    // Update ans
    sumOfExp += ans_sub;
  }
  // Base case
  if (N == 1)
    cout << S;
  else
 
    // Print answer
    cout << sumOfExp;
}
// Driver Code
 
int main()
{
  // Given string
  string S = "9999999999";
 
  // Length of the string
  int N = S.length();
 
  // Function call
  findSumOfExpressions(S, N);
}
 
// This code is contributed by phasing17.


Java




import java.util.List;
import java.util.ArrayList;
 
class Main
{
   
  // Function to find sum of all expressions by
  // inserting '+' operator at all possible indices
  static void findSumOfExpressions(String S, int N)
  {
     
    // Stores sum of all expressions by inserting
    // '+' operator at all possible indices
    long sumOfExp = 0;
 
    // Generate all possible subset
    // of indices iteratively
    for (int i = 0; i < Math.pow(2, N - 1); i++) {
      // Stores sum of
      // current expressions
      long ans_sub = 0;
 
      // Stores numbers of
      // current expressions
      String subst = "" + S.charAt(0);
 
      // Traverse the string at insert + at
      // current subset of indices
      for (int j = 0; j < N - 1; j++) {
        // If current index exists
        // in the current subset
        if (((i >> j) & 1) == 1) {
          // Update ans_sub
          ans_sub += Long.parseLong(subst);
 
          // Update subset
          subst = "" + S.charAt(j + 1);
        }
        else
          // Update subset
          subst += S.charAt(j + 1);
 
        // + can't be inserted after
        // the last index
        if (j == N - 2)
          ans_sub += Long.parseLong(subst);
      }
 
      // Update ans
      sumOfExp += ans_sub;
    }
    // Base case
    if (N == 1)
      System.out.println(S);
    else
 
      // Print answer
      System.out.println(sumOfExp);
  }
  // Driver Code
 
  public static void main(String[] args)
  {
     
    // Given string
    String S = "9999999999";
 
    // Length of the string
    int N = S.length();
 
    // Function call
    findSumOfExpressions(S, N);
  }
}
 
// This code is contributed by phasing17.


Python3




# Python program to implement
# the above approach
 
# Function to find sum of all expressions by
# inserting '+' operator at all possible indices
def findSumOfExpressions(S, N):
 
    # Stores sum of all expressions by inserting
    # '+' operator at all possible indices
    sumOfExp = 0
 
    # Generate all possible subset
    # of indices iteratively
    for i in range(2 ** (N - 1)):
 
        # Stores sum of
        # current expressions
        ans_sub = 0
 
        # Stores numbers of
        # current expressions
        subst = S[0]
 
        # Traverse the string at insert + at
        # current subset of indices
        for j in range(N - 1):
 
            # If current index exists
            # in the current subset
            if (i >> j) & 1:
 
                # Update ans_sub
                ans_sub += int(subst)
 
                # Update subset
                subst = S[j + 1]
            else:
 
                # Update subset
                subst += S[j + 1]
 
            # + can't be inserted after
            # the last index   
            if j == N - 2:
                ans_sub += int(subst)
 
        # Update ans
        sumOfExp += ans_sub
 
    # Base case    
    if N == 1:
        print(int(S))
    else:
 
        # Print answer
        print(sumOfExp)
 
# Driver Code
if __name__ == '__main__':
     
    # Given string
    S = "9999999999"
     
    # Length of the string
    N = len(S)
 
    # Function call
    findSumOfExpressions(S, N)


C#




// C# program to implement
// the above approach
using System;
using System.Collections.Generic;
 
class GFG
{
    // Function to find sum of all expressions by
    // inserting '+' operator at all possible indices
    static void findSumOfExpressions(string S, int N)
    {
       
      // Stores sum of all expressions by inserting
      // '+' operator at all possible indices
      ulong sumOfExp = 0;
     
      // Generate all possible subset
      // of indices iteratively
      for (int i = 0; i < Math.Pow(2, N - 1); i++) {
        // Stores sum of
        // current expressions
        ulong ans_sub = 0;
     
        // Stores numbers of
        // current expressions
        string subst = "" + S[0];
     
        // Traverse the string at insert + at
        // current subset of indices
        for (int j = 0; j < N - 1; j++) {
          // If current index exists
          // in the current subset
          if (((i >> j) & 1) == 1) {
            // Update ans_sub
            ans_sub += Convert.ToUInt64(subst);
     
            // Update subset
            subst = "" + S[j + 1];
          }
          else
            // Update subset
            subst += S[j + 1];
     
          // + can't be inserted after
          // the last index
          if (j == N - 2)
            ans_sub += Convert.ToUInt64(subst);
        }
     
        // Update ans
        sumOfExp += ans_sub;
      }
      // Base case
      if (N == 1)
        Console.WriteLine(S);
      else
     
        // Print answer
        Console.WriteLine(sumOfExp);
    }
    // Driver Code
     
    public static void Main(string[] args)
    {
      // Given string
      string S = "9999999999";
     
      // Length of the string
      int N = S.Length;
     
      // Function call
      findSumOfExpressions(S, N);
    }
}
 
// This code is contributed by phasing17.


Javascript




// JavaScript program to implement
// the above approach
 
// Function to find sum of all expressions by
// inserting '+' operator at all possible indices
function findSumOfExpressions(S, N)
{
    // Stores sum of all expressions by inserting
    // '+' operator at all possible indices
    let sumOfExp = 0
 
    // Generate all possible subset
    // of indices iteratively
    for (var i = 0; i < 2 ** (N - 1); i++)
    {
        // Stores sum of
        // current expressions
        let ans_sub = 0
 
        // Stores numbers of
        // current expressions
        let subst = S[0]
 
        // Traverse the string at insert + at
        // current subset of indices
        for (var j = 0; j < N - 1; j++)
        {
            // If current index exists
            // in the current subset
            if (((i >> j) & 1) == 1)
            {
                // Update ans_sub
                ans_sub += parseInt(subst)
 
                // Update subset
                subst = S[j + 1]
            }
            else
 
                // Update subset
                subst += S[j + 1]
 
            // + can't be inserted after
            // the last index   
            if (j == N - 2)
                ans_sub += parseInt(subst)
        }
        // Update ans
        sumOfExp += ans_sub
    }
    // Base case    
    if (N == 1)
        console.log(parseInt(S))
    else
 
        // Print answer
        console.log(sumOfExp)
}
// Driver Code
 
// Given string
let S = "9999999999"
     
// Length of the string
let N = S.length
 
// Function call
findSumOfExpressions(S, N)
 
// This code is contributed by phasing17.


Output:

12656242944

Time Complexity: O(2N * N)
Auxiliary Space: O(1)


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