Choose maximum weight with given weight and value ratio

Given weights and values of n items and a value k. We need to choose a subset of these items in such a way that ratio of the sum of weight and sum of values of chosen items is K and sum of weight is maximum among all possible subset choices.

Input : weight[] = [4, 8, 9]
        values[] = [2, 4, 6]
        K = 2
Output : 12
We can choose only first and second item only, 
because (4 + 8) / (2 + 4) = 2 which is equal to K
we can't include third item with weight 9 because 
then ratio condition won't be satisfied so result 
will be (4 + 8) = 12

We can solve this problem using dynamic programming. We can make a 2 state dp where dp(i, j) will store maximum possible sum of weights under given conditions when total items are N and required ratio is K.
Now in two states of dp, we will store the last item chosen and the difference between sum of weight and sum of values. We will multiply item values by K so that second state of dp will actually store (sum of weight – K*(sum of values)) for chosen items. Now we can see that our answer will be stored in dp(N-1, 0) because as last item is (N-1)th so all items are being considered and difference between sum of weight and K*(sum of values) is 0 that means sum of weight and sum of values has a ratio K.
After defining above dp state we can write transition among states simply as shown below,

dp(last, diff) = max (dp(last - 1, diff),    
                 dp(last-1, diff + wt[last] - val[last]*K))

dp(last – 1, diff) represents the condition when current
                   item is not chosen and 
dp(last – 1, diff + wt[last] – val[last] * K)) represents 
the condition when current item is chosen so difference 
is updated with weight and value of current item.

In below code a top-down approach is used for solving this dynamic programming and for storing dp states a map is used because the difference can be negative also and the 2D array can create problem in that case and special care need to be taken.

C++

// C++ program to choose item with maximum
// sum of weight under given constraint
#include <bits/stdc++.h>
using namespace std;

// memoized recursive method to return maximum
// weight with K as ratio of weight and values
int maxWeightRec(int wt[], int val[], int K,
                  map<pair<int, int>, int>& mp,
                            int last, int diff)
{
    //  base cases : if no item is remaining
    if (last == -1)
    {
        if (diff == 0)
            return 0;
        else
            return INT_MIN;
    }

    // first make pair with last chosen item and
    // difference between weight and values
    pair<int, int> tmp = make_pair(last, diff);
    if (mp.find(tmp) != mp.end())
        return mp[tmp];

    /*  choose maximum value from following two
        1) not selecting the current item and calling
           recursively
        2) selection current item, including the weight
           and updating the difference before calling
           recurively */
    mp[tmp] = max(maxWeightRec(wt, val, K, mp, last - 1, diff),
                   wt[last] + maxWeightRec(wt, val, K, mp,
                   last - 1, diff + wt[last] - val[last] * K));

    return mp[tmp];
}

// method returns maximum sum of weight with K
// as ration of sum of weight and their values
int maxWeight(int wt[], int val[], int K, int N)
{
    map<pair<int, int>, int> mp;
    return maxWeightRec(wt, val, K, mp, N - 1, 0);
}

//  Driver code to test above methods
int main()
{
    int wt[] = {4, 8, 9};
    int val[] = {2, 4, 6};
    int N = sizeof(wt) / sizeof(int);
    int K = 2;

    cout << maxWeight(wt, val, K, N);
    return 0;
}

Java

// Java program to choose item with maximum
// sum of weight under given constraint

import java.awt.Point;
import java.util.HashMap;

class Test
{
	// memoized recursive method to return maximum
	// weight with K as ratio of weight and values
	static int maxWeightRec(int wt[], int val[], int K,
	                  HashMap<Point, Integer> hm,
	                            int last, int diff)
	{
	    //  base cases : if no item is remaining
	    if (last == -1)
	    {
	        if (diff == 0)
	            return 0;
	        else
	            return Integer.MIN_VALUE;
	    }
	 
	    // first make pair with last chosen item and
	    // difference between weight and values
	    Point tmp = new Point(last, diff);
	    if (hm.containsKey(tmp))
	        return hm.get(tmp);
	 
	    /*  choose maximum value from following two
	        1) not selecting the current item and calling
	           recursively
	        2) selection current item, including the weight
	           and updating the difference before calling
	           recursively */
	   hm.put(tmp,Math.max(maxWeightRec(wt, val, K, hm, last - 1, diff),
	                   wt[last] + maxWeightRec(wt, val, K, hm,
	                   last - 1, diff + wt[last] - val[last] * K)));
	 
	    return hm.get(tmp);
	}
	 
	// method returns maximum sum of weight with K
	// as ration of sum of weight and their values
	static int maxWeight(int wt[], int val[], int K, int N)
	{
	    HashMap<Point, Integer> hm = new HashMap<>();
	    return maxWeightRec(wt, val, K, hm, N - 1, 0);
	}
	
	// Driver method
	public static void main(String args[])
	{
		int wt[] = {4, 8, 9};
	    int val[] = {2, 4, 6};
	    
	    int K = 2;
	 
	    System.out.println(maxWeight(wt, val, K, wt.length));
	}
}
// This code is contributed by Gaurav Miglani


Output:

12

This article is contributed by Utkarsh Trivedi. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

GATE CS Corner    Company Wise Coding Practice

Recommended Posts:







Writing code in comment? Please use ide.geeksforgeeks.org, generate link and share the link here.