Smallest subset of maximum sum possible by splitting array into two subsets

Given an array arr[] consisting of N integers, the task is to print the smaller of the two subsets obtained by splitting the array into two subsets such that the sum of the smaller subset is maximized.

Examples:

Input: arr[] = {5, 3, 2, 4, 1, 2}
Output: 4 5
Explanation:
Split the array into two subsets as {4, 5} and {1, 2, 2, 3}.
The subset {4, 5} is of minimum length, i.e. 2, having maximum sum = 4 + 5 = 9.

Input: arr[] = {20, 15, 20, 50, 20}
Output: 15 50

Approach: The given problem can be solved by using Hashing and Sorting. 
Follow the steps below to solve the problem:

• Initialize a HashMap, say M, to store the frequency of each character of the array arr[].
• Traverse the array arr[] and increment the count of every character in the HashMap M.
• Initialize 2 variables, say S, and flag, to store the sum of the first subset and to store if an answer exists or not respectively.
• Sort the array arr[] in ascending order.
• Initialize an ArrayList, say ans, to store the elements of the resultant subset.
• Traverse the array arr[] in reverse order and perform the following steps:
  • Store the frequency of the current character in a variable, say F.
  • If (F + ans.size()) is less than (N – (F + ans.size())) then append the element arr[i] in the ArrayList ans F number of times.
  • Decrement the value of i by F.
  • If the value of S is greater than the sum of the array elements, then mark the flag as true and then break.
• After completing the above steps, if the value of flag is true, then print the ArrayList ans as the resultant subset. Otherwise, print -1.the

Below is the implementation of the above approach:

C++

// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;

// Function to split array elements
// into two subsets having sum of
// the smaller subset maximized
static void findSubset(vector<int> arr)
{

    // Stores the size of the array
    int N = arr.size();

    // Stores the frequency
    // of array elements
    map<int,int> mp;

    // Stores the total
    // sum of the array
    int totSum = 0;

    // Stores the sum of
    // the resultant set
    int s = 0;

    // Stores if it is possible
    // to split the array that
    // satisfies the conditions
    int flag = 0;

    // Stores the elements
    // of the first subseta
    vector<int> ans;

    // Traverse the array arr[]
    for (int i = 0;
         i < arr.size(); i++) {

        // Increment total sum
        totSum += arr[i];

        // Increment count of arr[i]
        mp[arr[i]]=mp[arr[i]]+1;
      }

    // Sort the array arr[]
    sort(arr.begin(),arr.end());

    // Stores the index of the
    // last element of the array
    int i = N - 1;

    // Traverse the array arr[]
    while (i >= 0) {

        // Stores the frequency
        // of arr[i]
        int frq = mp[arr[i]];

        // If frq + ans.size() is
        // at most remaining size
        if ((frq + ans.size())
            < (N - (frq + ans.size())))
        {

            for (int k = 0; k < frq; k++)
            {

                // Append arr[i] to ans
                ans.push_back(arr[i]);

                // Decrement totSum by arr[i]
                totSum -= arr[i];

                // Increment s by arr[i]
                s += arr[i];

                i--;
            }
        }

        // Otherwise, decrement i
        // by frq
        else {
            i -= frq;
        }

        // If s is greater
        // than totSum
        if (s > totSum) {

            // Mark flag 1
            flag = 1;
            break;
        }
    }

    // If flag is equal to 1
    if (flag == 1) {

        // Print the arrList ans
        for (i = ans.size() - 1;
             i >= 0; i--) {

            cout<<ans[i]<<" ";
        }
    }

    // Otherwise, print "-1"
    else {
        cout<<-1;
    }
}

// Driver Code
int main()
{
    vector<int> arr = { 5, 3, 2, 4, 1, 2 };
    findSubset(arr);
}

// This code is contributed by mohit kumar 29.

Java

// Java program for above approach

import java.io.*;
import java.lang.*;
import java.util.*;

class GFG {

    // Function to split array elements
    // into two subsets having sum of
    // the smaller subset maximized
    static void findSubset(int[] arr)
    {
        // Stores the size of the array
        int N = arr.length;

        // Stores the frequency
        // of array elements
        Map<Integer, Integer> map
            = new HashMap<>();

        // Stores the total
        // sum of the array
        int totSum = 0;

        // Stores the sum of
        // the resultant set
        int s = 0;

        // Stores if it is possible
        // to split the array that
        // satisfies the conditions
        int flag = 0;

        // Stores the elements
        // of the first subset
        ArrayList<Integer> ans
            = new ArrayList<>();

        // Traverse the array arr[]
        for (int i = 0;
             i < arr.length; i++) {

            // Increment total sum
            totSum += arr[i];

            // Increment count of arr[i]
            map.put(arr[i],
                    map.getOrDefault(
                        arr[i], 0)
                        + 1);
        }

        // Sort the array arr[]
        Arrays.sort(arr);

        // Stores the index of the
        // last element of the array
        int i = N - 1;

        // Traverse the array arr[]
        while (i >= 0) {

            // Stores the frequency
            // of arr[i]
            int frq = map.get(arr[i]);

            // If frq + ans.size() is
            // at most remaining size
            if ((frq + ans.size())
                < (N - (frq + ans.size()))) {

                for (int k = 0; k < frq; k++) {

                    // Append arr[i] to ans
                    ans.add(arr[i]);

                    // Decrement totSum by arr[i]
                    totSum -= arr[i];

                    // Increment s by arr[i]
                    s += arr[i];

                    i--;
                }
            }

            // Otherwise, decrement i
            // by frq
            else {
                i -= frq;
            }

            // If s is greater
            // than totSum
            if (s > totSum) {

                // Mark flag 1
                flag = 1;
                break;
            }
        }

        // If flag is equal to 1
        if (flag == 1) {

            // Print the arrList ans
            for (i = ans.size() - 1;
                 i >= 0; i--) {

                System.out.print(
                    ans.get(i) + " ");
            }
        }

        // Otherwise, print "-1"
        else {
            System.out.print(-1);
        }
    }

    // Driver Code
    public static void main(String[] args)
    {
        int[] arr = { 5, 3, 2, 4, 1, 2 };
        findSubset(arr);
    }
}

Python3

# Python 3 program for the above approach
from collections import defaultdict

# Function to split array elements
# into two subsets having sum of
# the smaller subset maximized
def findSubset(arr):

    # Stores the size of the array
    N = len(arr)

    # Stores the frequency
    # of array elements
    mp = defaultdict(int)

    # Stores the total
    # sum of the array
    totSum = 0

    # Stores the sum of
    # the resultant set
    s = 0

    # Stores if it is possible
    # to split the array that
    # satisfies the conditions
    flag = 0

    # Stores the elements
    # of the first subseta
    ans = []

    # Traverse the array arr[]
    for i in range(len(arr)):

        # Increment total sum
        totSum += arr[i]

        # Increment count of arr[i]
        mp[arr[i]] = mp[arr[i]]+1

    # Sort the array arr[]
    arr.sort()

    # Stores the index of the
    # last element of the array
    i = N - 1

    # Traverse the array arr[]
    while (i >= 0):

        # Stores the frequency
        # of arr[i]
        frq = mp[arr[i]]

        # If frq + ans.size() is
        # at most remaining size
        if ((frq + len(ans))
                < (N - (frq + len(ans)))):

            for k in range(frq):

                # Append arr[i] to ans
                ans.append(arr[i])

                # Decrement totSum by arr[i]
                totSum -= arr[i]

                # Increment s by arr[i]
                s += arr[i]
                i -= 1

        # Otherwise, decrement i
        # by frq
        else:
            i -= frq

        # If s is greater
        # than totSum
        if (s > totSum):

            # Mark flag 1
            flag = 1
            break

    # If flag is equal to 1
    if (flag == 1):

        # Print the arrList ans
        for i in range(len(ans) - 1, -1, -1):

            print(ans[i], end = " ")

    # Otherwise, print "-1"
    else:
        print(-1)

# Driver Code
if __name__ == "__main__":

    arr = [5, 3, 2, 4, 1, 2]
    findSubset(arr)

    # This code is contributed by ukasp.

C#

// C# program for the above approach
using System;
using System.Collections.Generic;

class GFG{

// Function to split array elements
// into two subsets having sum of
// the smaller subset maximized
static void findSubset(List<int> arr)
{

    // Stores the size of the array
    int N = arr.Count;
    int i;

    // Stores the frequency
    // of array elements
    Dictionary<int,int> mp = new Dictionary<int,int>();

    // Stores the total
    // sum of the array
    int totSum = 0;

    // Stores the sum of
    // the resultant set
    int s = 0;

    // Stores if it is possible
    // to split the array that
    // satisfies the conditions
    int flag = 0;

    // Stores the elements
    // of the first subseta
    List<int> ans = new List<int>();

    // Traverse the array arr[]
    for (i = 0;
         i < arr.Count; i++) {

        // Increment total sum
        totSum += arr[i];

        // Increment count of arr[i]
        if(mp.ContainsKey(arr[i]))
         mp[arr[i]]=mp[arr[i]]+1;
        else
          mp.Add(arr[i],1);
      }

    // Sort the array arr[]
    arr.Sort();

    // Stores the index of the
    // last element of the array
    i = N - 1;

    // Traverse the array arr[]
    while (i >= 0) {

        // Stores the frequency
        // of arr[i]
        int frq = mp[arr[i]];

        // If frq + ans.size() is
        // at most remaining size
        if ((frq + ans.Count)
            < (N - (frq + ans.Count)))
        {

            for (int k = 0; k < frq; k++)
            {

                // Append arr[i] to ans
                ans.Add(arr[i]);

                // Decrement totSum by arr[i]
                totSum -= arr[i];

                // Increment s by arr[i]
                s += arr[i];

                i--;
            }
        }

        // Otherwise, decrement i
        // by frq
        else {
            i -= frq;
        }

        // If s is greater
        // than totSum
        if (s > totSum) {

            // Mark flag 1
            flag = 1;
            break;
        }
    }

    // If flag is equal to 1
    if (flag == 1) {

        // Print the arrList ans
        for (i = ans.Count - 1;
             i >= 0; i--) {

            Console.Write(ans[i]+" ");
        }
    }

    // Otherwise, print "-1"
    else {
        Console.Write(-1);
    }
}

// Driver Code
public static void Main()
{
    List<int> arr = new List<int>(){ 5, 3, 2, 4, 1, 2 };
    findSubset(arr);
}

}

// This code is contributed by ipg2016107.

Javascript

<script>

// Javascript program for the above approach


// Function to split array elements
// into two subsets having sum of
// the smaller subset maximized
function findSubset(arr)
{

    // Stores the size of the array
    var N = arr.length;

    // Stores the frequency
    // of array elements
    var mp = new Map();

    // Stores the total
    // sum of the array
    var totSum = 0;

    // Stores the sum of
    // the resultant set
    var s = 0;

    // Stores if it is possible
    // to split the array that
    // satisfies the conditions
    var flag = 0;

    // Stores the elements
    // of the first subseta
    var ans = [];

    // Traverse the array arr[]
    for (var i = 0;
         i < arr.length; i++) {

        // Increment total sum
        totSum += arr[i];

        // Increment count of arr[i]
        if(mp.has(arr[i]))
            mp.set(arr[i], mp.get(arr[i])+1)
        else
            mp.set(arr[i], 1);
      }

    // Sort the array arr[]
    arr.sort((a,b)=> a-b)

    // Stores the index of the
    // last element of the array
    var i = N - 1;

    // Traverse the array arr[]
    while (i >= 0) {

        // Stores the frequency
        // of arr[i]
        var frq = mp.get(arr[i]);

        // If frq + ans.size() is
        // at most remaining size
        if ((frq + ans.length)
            < (N - (frq + ans.length)))
        {

            for (var k = 0; k < frq; k++)
            {

                // Append arr[i] to ans
                ans.push(arr[i]);

                // Decrement totSum by arr[i]
                totSum -= arr[i];

                // Increment s by arr[i]
                s += arr[i];

                i--;
            }
        }

        // Otherwise, decrement i
        // by frq
        else {
            i -= frq;
        }

        // If s is greater
        // than totSum
        if (s > totSum) {

            // Mark flag 1
            flag = 1;
            break;
        }
    }

    // If flag is equal to 1
    if (flag == 1) {

        // Print the arrList ans
        for (i = ans.length - 1;
             i >= 0; i--) {

            document.write( ans[i] + " ");
        }
    }

    // Otherwise, print "-1"
    else {
        document.write(-1);
    }
}

// Driver Code
var arr = [5, 3, 2, 4, 1, 2 ];
findSubset(arr);

// This code is contributed by rutvik_56.
</script>

Output:

4 5

Time Complexity: O(N*log N)
Auxiliary Space: O(N)