# Print equal sum sets of array (Partition Problem) | Set 2

• Difficulty Level : Hard
• Last Updated : 22 Apr, 2021

Given an array arr[]. Determine whether it is possible to split the array into two sets such that the sum of elements in both sets is equal. If it is possible, then print both sets. If it is not possible then output -1.
Examples :

```Input : arr = {5, 5, 1, 11}
Output : Set 1 = {5, 5, 1}, Set 2 = {11}
Sum of both the sets is 11 and equal.

Input : arr = {1, 5, 3}
Output : -1
No partitioning results in equal sum sets.```

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Prerequisite: Partition Problem
Approach: In the previous post, a solution using recursion is discussed. In this post, a solution using Dynamic Programming is explained.
The idea is to declare two sets set 1 and set 2. To recover the solution, traverse the boolean dp table backward starting from the final result dp[n][k], where n = number of elements and k = sum/2. Set 1 will consist of elements that contribute to sum k and other elements that do not contribute are added to set 2. Follow these steps at each position to recover the solution.

1. Check if dp[i-1][sum] is true or not. If it is true, then the current element does not contribute to sum k. Add this element to set 2. Update index i by i-1 and sum remains unchanged.

2. If dp[i-1][sum] is false, then current element contribute to sum k. Add current element to set 1. Update index i by i-1 and sum by sum-arr[i-1].

Repeat the above steps until each index position is traversed.
Implementation:

## C++

 `// CPP program to print equal sum sets of array.``#include ``using` `namespace` `std;` `// Function to print equal sum``// sets of array.``void` `printEqualSumSets(``int` `arr[], ``int` `n)``{``    ``int` `i, currSum;``   ` `    ``// Finding sum of array elements``    ``int` `sum = accumulate(arr, arr+n, 0);` `    ``// Check sum is even or odd. If odd``    ``// then array cannot be partitioned.``    ``// Print -1 and return.``    ``if` `(sum & 1) {``        ``cout << ``"-1"``;``        ``return``;``    ``}` `    ``// Divide sum by 2 to find``    ``// sum of two possible subsets.``    ``int` `k = sum >> 1;` `    ``// Boolean DP table to store result``    ``// of states.``    ``// dp[i][j] = true if there is a``    ``// subset of elements in first i elements``    ``// of array that has sum equal to j.``    ``bool` `dp[n + 1][k + 1];` `    ``// If number of elements are zero, then``    ``// no sum can be obtained.``    ``for` `(i = 1; i <= k; i++)``        ``dp[0][i] = ``false``;` `    ``// Sum 0 can be obtained by not selecting``    ``// any element.``    ``for` `(i = 0; i <= n; i++)``        ``dp[i][0] = ``true``;` `    ``// Fill the DP table in bottom up manner.``    ``for` `(i = 1; i <= n; i++) {``        ``for` `(currSum = 1; currSum <= k; currSum++) {` `            ``// Excluding current element.``            ``dp[i][currSum] = dp[i - 1][currSum];` `            ``// Including current element``            ``if` `(arr[i - 1] <= currSum)``                ``dp[i][currSum] = dp[i][currSum] |``                  ``dp[i - 1][currSum - arr[i - 1]];``        ``}``    ``}` `    ``// Required sets set1 and set2.``    ``vector<``int``> set1, set2;` `    ``// If partition is not possible print``    ``// -1 and return.``    ``if` `(!dp[n][k]) {``        ``cout << ``"-1\n"``;``        ``return``;``    ``}` `    ``// Start from last element in dp table.``    ``i = n;``    ``currSum = k;` `    ``while` `(i > 0 && currSum >= 0) {` `        ``// If current element does not``        ``// contribute to k, then it belongs``        ``// to set 2.``        ``if` `(dp[i - 1][currSum]) {``            ``i--;``            ``set2.push_back(arr[i]);``        ``}` `        ``// If current element contribute``        ``// to k then it belongs to set 1.``        ``else` `if` `(dp[i - 1][currSum - arr[i - 1]]) {``            ``i--;``            ``currSum -= arr[i];``            ``set1.push_back(arr[i]);``        ``}``    ``}` `    ``// Print elements of both the sets.``    ``cout << ``"Set 1 elements: "``;``    ``for` `(i = 0; i < set1.size(); i++)``        ``cout << set1[i] << ``" "``;``    ``cout << ``"\nSet 2 elements: "``;``    ``for` `(i = 0; i < set2.size(); i++)``        ``cout << set2[i] << ``" "``;   ``}` `// Driver program.``int` `main()``{``    ``int` `arr[] = { 5, 5, 1, 11 };``    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``printEqualSumSets(arr, n);``    ``return` `0;``}`

## Java

 `// Java program to print``// equal sum sets of array.``import` `java.io.*;``import` `java.util.*;` `class` `GFG``{``    ``// Function to print equal``    ``// sum sets of array.``    ``static` `void` `printEqualSumSets(``int` `[]arr,``                                  ``int` `n)``    ``{``        ``int` `i, currSum, sum = ``0``;``        ` `        ``// Finding sum of array elements``        ``for` `(i = ``0``; i < arr.length; i++)``            ``sum += arr[i];``    ` `        ``// Check sum is even or odd.``        ``// If odd then array cannot``        ``// be partitioned. Print -1``        ``// and return.``        ``if` `((sum & ``1``) == ``1``)``        ``{``            ``System.out.print(``"-1"``);``            ``return``;``        ``}``    ` `        ``// Divide sum by 2 to find``        ``// sum of two possible subsets.``        ``int` `k = sum >> ``1``;``    ` `        ``// Boolean DP table to store``        ``// result of states.``        ``// dp[i,j] = true if there is a``        ``// subset of elements in first i``        ``// elements of array that has sum``        ``// equal to j.``        ``boolean` `[][]dp = ``new` `boolean``[n + ``1``][k + ``1``];``    ` `        ``// If number of elements are zero,``        ``// then no sum can be obtained.``        ``for` `(i = ``1``; i <= k; i++)``            ``dp[``0``][i] = ``false``;``    ` `        ``// Sum 0 can be obtained by``        ``// not selecting any element.``        ``for` `(i = ``0``; i <= n; i++)``            ``dp[i][``0``] = ``true``;``    ` `        ``// Fill the DP table``        ``// in bottom up manner.``        ``for` `(i = ``1``; i <= n; i++)``        ``{``            ``for` `(currSum = ``1``;``                 ``currSum <= k;``                 ``currSum++)``            ``{``    ` `                ``// Excluding current element.``                ``dp[i][currSum] = dp[i - ``1``][currSum];``    ` `                ``// Including current element``                ``if` `(arr[i - ``1``] <= currSum)``                    ``dp[i][currSum] = dp[i][currSum] |``                    ``dp[i - ``1``][currSum - arr[i - ``1``]];``            ``}``        ``}``    ` `        ``// Required sets set1 and set2.``        ``List set1 = ``new` `ArrayList();``        ``List set2 = ``new` `ArrayList();``    ` `        ``// If partition is not possible``        ``// print -1 and return.``        ``if` `(!dp[n][k])``        ``{``            ``System.out.print(``"-1\n"``);``            ``return``;``        ``}``    ` `        ``// Start from last``        ``// element in dp table.``        ``i = n;``        ``currSum = k;``    ` `        ``while` `(i > ``0` `&& currSum >= ``0``)``        ``{``    ` `            ``// If current element does``            ``// not contribute to k, then``            ``// it belongs to set 2.``            ``if` `(dp[i - ``1``][currSum])``            ``{``                ``i--;``                ``set2.add(arr[i]);``            ``}``    ` `            ``// If current element contribute``            ``// to k then it belongs to set 1.``            ``else` `if` `(dp[i - ``1``][currSum - arr[i - ``1``]])``            ``{``                ``i--;``                ``currSum -= arr[i];``                ``set1.add(arr[i]);``            ``}``        ``}``    ` `        ``// Print elements of both the sets.``        ``System.out.print(``"Set 1 elements: "``);``        ``for` `(i = ``0``; i < set1.size(); i++)``            ``System.out.print(set1.get(i) + ``" "``);``            ` `        ``System.out.print(``"\nSet 2 elements: "``);``        ` `        ``for` `(i = ``0``; i < set2.size(); i++)``            ``System.out.print(set2.get(i) + ``" "``);``    ``}``    ` `    ``// Driver Code``    ``public` `static` `void` `main(String args[])``    ``{``        ``int` `[]arr = ``new` `int``[]{ ``5``, ``5``, ``1``, ``11` `};``        ``int` `n = arr.length;``        ``printEqualSumSets(arr, n);``    ``}``}` `// This code is contributed by``// Manish Shaw(manishshaw1)`

## Python3

 `# Python3 program to print equal sum``# sets of array.``import` `numpy as np` `# Function to print equal sum``# sets of array.``def` `printEqualSumSets(arr, n) :` `    ``# Finding sum of array elements``    ``sum_array ``=` `sum``(arr)` `    ``# Check sum is even or odd. If odd``    ``# then array cannot be partitioned.``    ``# Print -1 and return.``    ``if` `(sum_array & ``1``) :``        ``print``(``"-1"``)``        ``return``    ` `    ``# Divide sum by 2 to find``    ``# sum of two possible subsets.``    ``k ``=` `sum_array >> ``1` `    ``# Boolean DP table to store result``    ``# of states.``    ``# dp[i][j] = true if there is a``    ``# subset of elements in first i elements``    ``# of array that has sum equal to j.``    ``dp ``=` `np.zeros((n ``+` `1``, k ``+` `1``))` `    ``# If number of elements are zero, then``    ``# no sum can be obtained.``    ``for` `i ``in` `range``(``1``, k ``+` `1``) :``        ``dp[``0``][i] ``=` `False` `    ``# Sum 0 can be obtained by not``    ``# selecting any element.``    ``for` `i ``in` `range``(n ``+` `1``) :``        ``dp[i][``0``] ``=` `True` `    ``# Fill the DP table in bottom up manner.``    ``for` `i ``in` `range``(``1``, n ``+` `1``) :``        ``for` `currSum ``in` `range``(``1``, k ``+` `1``) :` `            ``# Excluding current element.``            ``dp[i][currSum] ``=` `dp[i ``-` `1``][currSum]` `            ``# Including current element``            ``if` `(arr[i ``-` `1``] <``=` `currSum) :``                ``dp[i][currSum] ``=` `(dp[i][currSum] ``or``                                  ``dp[i ``-` `1``][currSum ``-` `arr[i ``-` `1``]])` `    ``# Required sets set1 and set2.``    ``set1, set2 ``=` `[], []` `    ``# If partition is not possible print``    ``# -1 and return.``    ``if` `( ``not` `dp[n][k]) :``        ``print``(``"-1"``)``        ``return` `    ``# Start from last element in dp table.``    ``i ``=` `n``    ``currSum ``=` `k` `    ``while` `(i > ``0` `and` `currSum >``=` `0``) :` `        ``# If current element does not``        ``# contribute to k, then it belongs``        ``# to set 2.``        ``if` `(dp[i ``-` `1``][currSum]) :``            ``i ``-``=` `1``            ``set2.append(arr[i])``    ` `        ``# If current element contribute``        ``# to k then it belongs to set 1.``        ``elif` `(dp[i ``-` `1``][currSum ``-` `arr[i ``-` `1``]]) :``            ``i ``-``=` `1``            ``currSum ``-``=` `arr[i]``            ``set1.append(arr[i])` `    ``# Print elements of both the sets.``    ``print``(``"Set 1 elements:"``, end ``=` `" "``)``    ``for` `i ``in` `range``(``len``(set1)) :``        ``print``(set1[i], end ``=` `" "``)``        ` `    ``print``(``"\nSet 2 elements:"``, end ``=` `" "``)``    ``for` `i ``in` `range``(``len``(set2)) :``        ``print``(set2[i], end ``=` `" "``)    ` `# Driver Code``if` `__name__ ``=``=` `"__main__"` `:` `    ``arr ``=` `[ ``5``, ``5``, ``1``, ``11` `]``    ``n ``=` `len``(arr)``    ``printEqualSumSets(arr, n)` `# This code is contributed by Ryuga`

## C#

 `// C# program to print``// equal sum sets of array.``using` `System;``using` `System.Linq;``using` `System.Collections.Generic;` `class` `GFG``{``    ``// Function to print equal``    ``// sum sets of array.``    ``static` `void` `printEqualSumSets(``int` `[]arr,``                                  ``int` `n)``    ``{``        ``int` `i, currSum, sum = 0;``        ` `        ``// Finding sum of array elements``        ``for` `(i = 0; i < arr.Length; i++)``            ``sum += arr[i];``    ` `        ``// Check sum is even or odd.``        ``// If odd then array cannot``        ``// be partitioned. Print -1``        ``// and return.``        ``if` `((sum & 1) == 1)``        ``{``            ``Console.Write(``"-1"``);``            ``return``;``        ``}``    ` `        ``// Divide sum by 2 to find``        ``// sum of two possible subsets.``        ``int` `k = sum >> 1;``    ` `        ``// Boolean DP table to store``        ``// result of states.``        ``// dp[i,j] = true if there is a``        ``// subset of elements in first i``        ``// elements of array that has sum``        ``// equal to j.``        ``bool` `[,]dp = ``new` `bool``[n + 1, k + 1];``    ` `        ``// If number of elements are zero,``        ``// then no sum can be obtained.``        ``for` `(i = 1; i <= k; i++)``            ``dp[0, i] = ``false``;``    ` `        ``// Sum 0 can be obtained by``        ``// not selecting any element.``        ``for` `(i = 0; i <= n; i++)``            ``dp[i, 0] = ``true``;``    ` `        ``// Fill the DP table``        ``// in bottom up manner.``        ``for` `(i = 1; i <= n; i++)``        ``{``            ``for` `(currSum = 1; currSum <= k; currSum++)``            ``{``    ` `                ``// Excluding current element.``                ``dp[i, currSum] = dp[i - 1, currSum];``    ` `                ``// Including current element``                ``if` `(arr[i - 1] <= currSum)``                    ``dp[i, currSum] = dp[i, currSum] |``                    ``dp[i - 1, currSum - arr[i - 1]];``            ``}``        ``}``    ` `        ``// Required sets set1 and set2.``        ``List<``int``> set1 = ``new` `List<``int``>();``        ``List<``int``> set2 = ``new` `List<``int``>();``    ` `        ``// If partition is not possible``        ``// print -1 and return.``        ``if` `(!dp[n, k])``        ``{``            ``Console.Write(``"-1\n"``);``            ``return``;``        ``}``    ` `        ``// Start from last``        ``// element in dp table.``        ``i = n;``        ``currSum = k;``    ` `        ``while` `(i > 0 && currSum >= 0)``        ``{``    ` `            ``// If current element does``            ``// not contribute to k, then``            ``// it belongs to set 2.``            ``if` `(dp[i - 1, currSum])``            ``{``                ``i--;``                ``set2.Add(arr[i]);``            ``}``    ` `            ``// If current element contribute``            ``// to k then it belongs to set 1.``            ``else` `if` `(dp[i - 1, currSum - arr[i - 1]])``            ``{``                ``i--;``                ``currSum -= arr[i];``                ``set1.Add(arr[i]);``            ``}``        ``}``    ` `        ``// Print elements of both the sets.``        ``Console.Write(``"Set 1 elements: "``);``        ``for` `(i = 0; i < set1.Count; i++)``            ``Console.Write(set1[i] + ``" "``);``            ` `        ``Console.Write(``"\nSet 2 elements: "``);``        ` `        ``for` `(i = 0; i < set2.Count; i++)``            ``Console.Write(set2[i] + ``" "``);``    ``}``    ` `    ``// Driver Code.``    ``static` `void` `Main()``    ``{``        ``int` `[]arr = { 5, 5, 1, 11 };``        ``int` `n = arr.Length;``        ``printEqualSumSets(arr, n);``    ``}``}``// This cide is contributed by``// Manish Shaw(manishshaw1)`

## Javascript

 ``
Output :
```Set 1 elements: 1 5 5
Set 2 elements: 11```

Time Complexity: O(n*k), where k = sum(arr) / 2
Auxiliary Space: O(n*k)

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