Recursive 0-1 knapsack

Question

Here I have two functions for the recursive knapsack problem while knapsack() gives the correct output (i.e 220) but knapsack1() gives wrong value (i.e 60) .Can anyone please explain why?

#include<iostream>
#include<stdio.h>
using namespace std;

 long knapsack1(long w,long wt[],long val[],long n)
    {
        if(n==0||w==0)
        {
            return 0;
        }
        if (wt[n] > w)
        {
        n--;
        }
        else
        {
            return max(knapsack1(w,wt,val,n-1),val[n]+knapsack1(w-wt[n],wt,val,n-1));
        }
    }

 long knapsack(long w,long wt[],long val[],long n)
    {
        if(n==0||w==0)
        {
            return 0;
        }
        if (wt[n] > w)
        { 
       return knapsack(w, wt, val, n-1);
        }
        else
        {
            return max(knapsack(w,wt,val,n-1),val[n]+knapsack(w-wt[n],wt,val,n-1));
        }
    }
int main()
{
   long val[] = {60, 100, 120};
    long wt[] = {10, 20, 30};
    long  w = 50;
    long n = sizeof(val)/sizeof(val[0]);
    printf("%d", knapsack(w, wt, val, n));
    printf("%d", knapsack1(w, wt, val, n));
    return 0;
}

What have you learned through basic debugging? You should be able to describe what in your control and/or data flow isn't operating as expected. See this lovely [debug](https://ericlippert.com/2014/03/05/how-to-debug-small-programs/) blog for help. — Prune, Jun 01 '17 at 20:09

score 1 · Answer 1 · answered Jun 01 '17 at 18:52

1

Try compiling it with warnings enabled… the if-branch in knapsack1 does not return a value, and the behavior is undefined.

answered Jun 01 '17 at 18:52

Arne Vogel

6,346
2
18
31

Recursive 0-1 knapsack

1 Answers1