Question

I have written a code to calculate the minimum number of coins using Greedy algorithm and Dynamic algorithm, but the Dynamic algorithm part doesn’t work properly. There is a Null value going to array, I can’t find it. Please HELP me. I need a answer as soon as possible.

#include <stdio.h>
int n;
int denom[]={1,2,4,5,20,25};
int coinCounter(int n);
int main(){

     printf("Please Enter a Number : ");
     scanf("%d",&n);
    int coinmin,orin,i;
    orin=n;
    i=coinmin=0;
     for(i=(sizeof(denom)/4)-1;i>=0;i--){

         coinmin =coinmin+n/denom[i];
          n=n%denom[i];
      }

    printf("Coin Min By Greedy Algorithm : %d\n",coinmin);
    printf("Dynamic Algorithm : %d\n",coinCounter(orin));
    return 0;
}

int coinCounter(int n){
    int opt[n];
    int largest[n];
    int i,j,a;
    i=j=0;
    for(j=1;j<=n;j++){

        opt[j]=10000;
         //printf("xxn");
        for(i=(sizeof(denom)/4)-1;i>=0;i--){

            if(denom[i]==j){

                opt[j]=1;
                largest[j]=j;
            }
            else if(denom[i]<j){
                a=opt[j-denom[i]]+1;
            }
            if(a<opt[j]){
                opt[j]=a;
                largest[j]=denom[i];
            }
        }

    }
     return opt[n];

}

I edited the Code as following, but the answer is not coming

int coinCounter(int n){
    int opt[n];
    int largest[n];
    int i,j,a;
    i=j=0;
    for(j=1;j<n;j++){

        opt[j]=10000;
         printf("xxn");
        for(i=(sizeof(denom)/4)-1;i>=0;i--){

            if(denom[i]==j){

                opt[j]=1;
                largest[j]=j;
            }
            else if(denom[i]<j){
                a=opt[j-denom[i]]+1;
            }
            if(a<opt[j]){
                opt[j]=a;
                largest[j]=denom[i];
            }
        }

    }
     return opt[n-1];

}

hey these are the results I’m Getting

Please Enter a Number : 8
Coin Min By Greedy Algorithm : 3
Dynamic Algorithm : 1

Another answer I’m getting I can’t figure out what I’m doing wrong

Please Enter a Number : 71
Coin Min By Greedy Algorithm : 4
Dynamic Algorithm : 3

Answer 1

int coinCounter(int n){
    int opt[n];
    int largest[n]; <---- Don't do this. This does not work like you expect it to.

change to

int coinCounter(int n){
        int opt[n];
        int *largest = malloc(sizeof(int)*n);

Edit:

Another bug with the algorithm

your variable “a” is not initialized and you are using it in if condition.

think of the case when denom[i]>j
your variable “a” would not be initialized
so depending upon what garbage value it has , results will vary
bug is here , but it shows up when you change opt allocation, because that allocation changes the condition. What I want to say is – if (X<Y), depends on both X and Y. Problem is with X, but because you change Y, the condition changes and you get different result