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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

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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 ``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 > 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);``    ``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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