TheAlgorithms-C-Plus-Plus/greedy_algorithms/Knapsack.cpp

#include <iostream>
using namespace std;

struct Item
{
	int weight;
	int profit;
};

float profitPerUnit(Item x)
{
	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);
	}
}

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;
}