TheAlgorithms-C-Plus-Plus/Greedy Algorithms/Knapsack.cpp

#include<iostream>
using namespace std;

struct Item
{
	int weight;
	int profit;
};


float profitPerUnit(Item x)
{
//	cout<<(float)x.profit/(float)x.weight<<"\n";
	return (float)x.profit/(float)x.weight;
}

int partition (Item arr[], int low, int high)
{
    Item pivot = arr[high];    // pivot
    int i = (low - 1);  // Index of smaller element
 
    for (int j = low; j <high; j++)
    {
        // If current element is smaller than or
        // equal to pivot
        if (profitPerUnit(arr[j]) <= profitPerUnit(pivot))
        {
            i++;    // increment index of smaller element
            Item temp=arr[i];
            arr[i]=arr[j];
            arr[j]=temp;
        }
    }
    Item temp=arr[i+1];
    arr[i+1]=arr[high];
    arr[high]=temp;
    return (i + 1);
}
 

void quickSort(Item arr[], int low, int high)
{
    if (low < high)
    {
       
        int p= partition(arr, low, high);

        quickSort(arr, low, p - 1);
        quickSort(arr, p + 1, high);
    }
}
 



// void show(Item arr[], int size)
// {
//     for (int i=0; i < size; i++)
//     cout<<arr[i].weight<<"\t"<<arr[i].profit<<"\n";
// }


int main()
{
	cout<<"\nEnter the capacity of the knapsack : ";
	float capacity;
	cin>>capacity;
	cout<<"\n Enter the number of Items : ";
	int n;
	cin>>n;
	Item itemArray[n];
	for (int i = 0; i < n; i++)
	{
		cout<<"\nEnter the weight and profit of item "<<i+1<<" : ";
		cin>>itemArray[i].weight;
		cin>>itemArray[i].profit;
	}

	quickSort(itemArray, 0, n-1);

	// show(itemArray, n);

	float maxProfit=0;
	int i=n;
	while(capacity>0 && --i>=0)
	{
		if(capacity>=itemArray[i].weight)
		{
			maxProfit+=itemArray[i].profit;
			capacity-=itemArray[i].weight;
			cout<<"\n\t"<<itemArray[i].weight<<"\t"<<itemArray[i].profit;
		}
		else
		{
			maxProfit+=profitPerUnit(itemArray[i])*capacity;
			cout<<"\n\t"<<capacity<<"\t"<<profitPerUnit(itemArray[i])*capacity;
			capacity=0;
			break;
		}
	}

	cout<<"\nMax Profit : "<<maxProfit;

	return 0;
}