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Sort the numbers according to their sum of digits
  • Difficulty Level : Medium
  • Last Updated : 20 Feb, 2019

Given an array arr[] of N non-negative integers, the task is to sort these integers according to sum of their digits.

Examples:

Input: arr[] = {12, 10, 102, 31, 15}
Output: 10 12 102 31 15
10 => 1 + 0 = 1
12 => 1 + 2 = 3
102 => 1 + 0 + 2 = 3
31 => 3 + 1= 4
15 => 1 + 5 = 6

Input: arr[] = {14, 1101, 10, 35, 0}
Output: 0 10 1101 14 35

Approach: The idea is to store each element with its sum of digits in a vector pair and then sort all the elements of the vector according to the digit sums stored. Finally, print the elements in order.



Below is the implementation of the above approach:

C++




// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function to return the sum
// of the digits of n
int sumOfDigit(int n)
{
    int sum = 0;
    while (n > 0) {
        sum += n % 10;
        n = n / 10;
    }
    return sum;
}
  
// Function to sort the array according to
// the sum of the digits of elements
void sortArr(int arr[], int n)
{
    // Vector to store digit sum with respective element
    vector<pair<int, int> > vp;
  
    // Inserting digit sum with element in the vector pair
    for (int i = 0; i < n; i++) {
        vp.push_back(make_pair(sumOfDigit(arr[i]), arr[i]));
    }
  
    // Quick sort the vector, this will sort the pair
    // according to sum of the digits of elements
    sort(vp.begin(), vp.end());
  
    // Print the sorted vector content
    for (int i = 0; i < vp.size(); i++)
        cout << vp[i].second << " ";
}
  
// Driver code
int main()
{
    int arr[] = { 14, 1101, 10, 35, 0 };
    int n = sizeof(arr) / sizeof(arr[0]);
    sortArr(arr, n);
  
    return 0;
}

Python3




# Python3 implementation of the approach 
  
# Function to return the sum 
# of the digits of n 
def sumOfDigit(n) : 
      
    sum = 0
    while (n > 0) :
          
        sum += n % 10
        n = n // 10
          
    return sum
  
# Function to sort the array according to 
# the sum of the digits of elements 
def sortArr(arr, n) :
      
    # Vector to store digit sum with 
    # respective element 
    vp = []; 
  
    # Inserting digit sum with element
    # in the vector pair 
    for i in range(n) :
        vp.append([sumOfDigit(arr[i]), arr[i]]); 
  
    # Quick sort the vector, this will 
    # sort the pair according to sum 
    # of the digits of elements 
    vp.sort()
  
    # Print the sorted vector content 
    for i in range(len(vp)) :
        print(vp[i][1], end = " "); 
  
# Driver code 
if __name__ == "__main__"
  
    arr = [14, 1101, 10, 35, 0]; 
    n = len(arr);
    sortArr(arr, n); 
  
# This code is contributed by Ryuga
Output:
0 10 1101 14 35

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