Fractional_knapsack.cpp

// C/C++ program to solve fractional Knapsack Problem 
#include <bits/stdc++.h> 
  
using namespace std; 
  
// Structure for an item which stores weight and corresponding 
// value of Item 
struct Item 
{ 
    int value, weight; 
  
    // Constructor 
    Item(int value, int weight) : value(value), weight(weight) 
    {} 
}; 
  
// Comparison function to sort Item according to val/weight ratio 
bool cmp(struct Item a, struct Item b) 
{ 
    double r1 = (double)a.value / a.weight; 
    double r2 = (double)b.value / b.weight; 
    return r1 > r2; 
} 
  
// Main greedy function to solve problem 
double fractionalKnapsack(int W, struct Item arr[], int n) 
{ 
    //    sorting Item on basis of ratio 
    sort(arr, arr + n, cmp); 
  
    //    Uncomment to see new order of Items with their ratio 
    /* 
    for (int i = 0; i < n; i++) 
    { 
        cout << arr[i].value << "  " << arr[i].weight << " : " 
             << ((double)arr[i].value / arr[i].weight) << endl; 
    } 
    */
  
    int curWeight = 0;  // Current weight in knapsack 
    double finalvalue = 0.0; // Result (value in Knapsack) 
  
    // Looping through all Items 
    for (int i = 0; i < n; i++) 
    { 
        // If adding Item won't overflow, add it completely 
        if (curWeight + arr[i].weight <= W) 
        { 
            curWeight += arr[i].weight; 
            finalvalue += arr[i].value; 
        } 
  
        // If we can't add current Item, add fractional part of it 
        else
        { 
            int remain = W - curWeight; 
            finalvalue += arr[i].value * ((double) remain / arr[i].weight); 
            break; 
        } 
    } 
  
    // Returning final value 
    return finalvalue; 
} 
  
// driver program to test above function 
int main() 
{ 
    int W = 50;   //    Weight of knapsack 
    Item arr[] = {{60, 10}, {100, 20}, {120, 30}}; 
  
    int n = sizeof(arr) / sizeof(arr[0]); 
  
    cout << "Maximum value we can obtain = "
         << fractionalKnapsack(W, arr, n); 
    return 0; 
}