I am trying to merge to arrays without sorting (add one then another) using pointer method but its just printing the first array and then garbage values. What i am trying to do is just combine 2 arrays in one big array. No sorting required(at least for now).
void getarray(int*,int);
int merge(int*,int*,int,int,int*);
main()
{
int a[10],b[10],c[20];
int i,j,n,m,size;
clrscr();
printf("Enter no. of elements in FIRST array: ");
scanf("%d",&n);
getarray(a,n);
printf("Enter no. of elements in SECOND array: ");
scanf("%d",&m);
getarray(b,m);
merge(a,b,n,m,c);
printf("\nMerged Array: \n");
for(i=0;i<n+m;i++)
{
printf("\t%d\t",c[i]);
}
getch();
return 0;
}
void getarray(int *x, int y)
{
int i;
for(i=0;i<y;i++)
{
scanf("%d",x+i);
}
}
int merge(int *a, int *b,int n,int m,int *c)
{
int i,j;
for(i=0;i<n;i++)
{
*(c+i) = *(a+i);
}
for(j=i;j<i+m;j++)
{
*(c+j) = *(b+j);
}
}
Alternatively you can use (assuming c is large enough):
void merge(int *a, int *b,int n,int m,int *c) {
memcpy(c, a, sizeof(int)*n);
memcpy(c+n, b, sizeof(int)*m);
}
You would need to include string.h.
int merge(int *a, int *b,int n,int m,int *c)
{
int i,j;
for(i=0;i<n;i++)
{
*(c+i) = *(a+i);
}
for(j=0;j<m;j++)
{
*(c+n+j) = *(b+j);
}
}
Related
I was working on QUICKSORT and I wrote this whole program by myself. The code is as follows
#include<stdio.h>
#include<stdlib.h>
void quicksort(int*,int,int);
int partition(int*,int,int);
swap(int*,int*);
int main()
{
int *arr,n,i;
printf("\nEnter the size of the array");
scanf("%d",&n);
arr=(int*)malloc(n*sizeof(int));
printf("\nEnter the elements of the array one by one");
for(i=0;i<n;i++)
{
scanf("%d",arr+i);
}
quicksort(arr,0,n-1);
printf("\nThe Sorted Array is as follows");
for(i=0;i<n;i++)
{
printf("%d",*(arr+i));
}
return 0;
}
void quicksort(int* arr,int a,int b)
{
int c;
if(a<b)
c=partition(arr,a,b);
quicksort(arr,a,c-1);
quicksort(arr,c+1,b);
}
int partition(int* arr,int a,int b)
{
int x,y,index=*(arr+b);
x=a,y=b-1;
while(x<y)
{
if(*(arr+x)<index)
{
x++;
}
if(index<*(arr+y))
{
y--;
}
swap((arr+x),(arr+y));
}
swap((arr+x),(arr+b));
return x;
}
swap(int *a,int *b)
{
int temp;
temp=*a;
*a=*b;
*b=temp;
}
I tried to run this program but after the array input it says segmentation error. I spent few minutes looking at the code and checked the code again and again but I do not seem to move anywhere.
can someone tell me where is the mistake.
What should be happening if a is greater than or equal to b? this should solve the segmentation problem.
void quicksort(int* arr, int a, int b) {
int c;
if (a < b) {
c = partition(arr,a,b);
quicksort(arr, a, c-1);
quicksort(arr, c+1, b);
}
}
I want to sort the given array using quicksort.
So I wrote this code in c for quicksort algorithm but its not giving me correct answer.Its giving me the same output as the input.
eg: If i give input as
3
2
1
then it is giving
Output:
3
2
1
Please help and tell me where is the mistake.
#include<stdio.h>
void quicksort(int a[],int p,int r);
int partition(int a[],int p,int r);
void swap(int a,int b);
int main()
{
int n,i,p,r;
printf("ENter no of elements");
scanf("%d",&n);
int a[n];
printf("ENter the elements");
for(i=1;i<=n;i++)
{
scanf("%d",&a[i]);
}
p=1;
r=n;
quicksort(a,1,n);
printf("\n");
for(i=1;i<=n;i++)
{
printf("%d\n",a[i]);
}
return 0;
}
void quicksort(int a[],int p,int r)
{
int q;
if(p<r)
{
q = partition(a,p,r);
quicksort(a,p,q-1);
quicksort(a,q+1,r);
}
}
int partition(int a[],int p,int r)
{
int x,i,j;
x=a[r];
i=p-1;
for(j=p;j<=r-1;j++)
{
if(a[j]<=x)
{
i=i+1;
swap(a[i],a[j]);
}
}
swap(a[i+1],a[r]);
return (i+1);
}
void swap(int a,int b)
{
int t;
t=a;
a=b;
b=t;
}
void swap(int a,int b)
This line is taking the two parameters as copies of the values. The swapping is done on he copies.
void swap(int* a, int* b)
This is the C-style of passing parameters by reference. You need to pass the references then:
swap(&a[i], &a[j]);
I had a doubt in using pointers
For example I made this swapping program and to swap so i have to use pointers in order to maintain same address where swapping is happening
#include<stdio.h>
int swap(int *x,int *y); //swapping function
int main()
{
int a,b;
scanf("%d %d",&a,&b);
printf("A->%d,B->%d\n",a,b); //print original array
swap(&a,&b); //pass by reference
printf("A->%d,B->%d\n",a,b); //print sorted array
}
int swap(int *x,int *y)
{
int temp; // Swapping
temp =*x;
*x=*y;
*y=temp;
}
Then I wrote a program for merge sort. Here I just passed the value (pass by value) in the funtions without using pointers but when I print the sorted array in the main function it is sorted.
#include<stdio.h>
void merge(int a[],int start,int mid,int end); //Sorting and merging lists
void mergesort(int a[],int start,int end); //Dividing the list
int main()
{
int size,i;
scanf("%d",&size);
int arr[size];
for(i=0;i<size;i++) //Input array
{
scanf("%d",&arr[i]);
}
printf("Array is: ");
for(i=0;i<size;i++)
{
printf("%d ",arr[i]); //print original array
}
printf("\n");
mergesort(arr,0,size-1); //Mergesort call-pass by value
printf("Sorted Array is: ");
for(i=0;i<size;i++)
{
printf("%d ",arr[i]); //print sorted array
}
printf("\n");
}
void mergesort(int a[],int start,int end)
{
int mid;
if(start<end)
{
mid=(start+end)/2; //calculating mid and dividing array recursively
mergesort(a,start,mid);
mergesort(a,mid+1,end);
merge(a,start,mid+1,end);
}
}
void merge(int a[],int start,int mid,int end)
{
int b[end]; //auxillary array
int i;
int p=start,q=mid,k=start;
while((p<mid) && (q<=end)) //comparing both list
{
if(a[p]<=a[q])
{
b[k++]=a[p++];
}
else
{
b[k++]=a[q++];
}
}
while(p<mid) //adding remaing items to auxillary array
{
b[k++]=a[p++];
}
while(q<=end) //adding remaing items to auxillary array
{
b[k++]=a[q++];
}
for(i=start;i<k;i++) //copying items from auxillary array to original array
{
a[i]=b[i];
}
}
Why is this happening ?
You can't directly pass arrays by value in C (best you can do is wrap a fixed-size array in a struct). In a parameter list int a[] is exactly equivalent to int *a.
So you are using pointers and that's why the array is sorted.
In C and similar languages the first array dimension of a function parameter is rewriten as a pointer. So your interfaces
void merge(int a[],int start,int mid,int end);
void mergesort(int a[],int start,int end);
are exactly the same as
void merge(int* a,int start,int mid,int end);
void mergesort(int* a,int start,int end);
So actually for arrays, you always pass an address to your function.
I don't know why you say:
Here I just passed the value (pass by value) in the funtions without using pointers.
because, when you use
mergesort(int a[],int start,int end)
merge(int a[],int start,int mid,int end)
Then a[] is as same as when you use *a. It is using the pointer way.
The following c program is a quicksort recursive program. Although I have written this code according to the Cormen explanation, yet it is incorrectly sorting the input.For example it is sorting the input 3,8,1 to 3,1,8. Thanks a lot in advance for finding the mistake
#include<stdio.h>
void printa(int a[],int size)
{
int i;
printf("\n");
for(i=0;i<size;i++)
{
printf("%d\n",a[i]);
}
}
void swap(int *a,int *b)
{
int temp;
temp=*a;
*a=*b;
*b=temp;
}
int partition(int a[],int p,int r)
{
int i,j,x;
i=p-1;
x=a[r];
for(j=p;j<r;j++)
{
if(a[j]<=x)
{
i=i+1;
swap(&a[i],&a[j]);
}
swap(&a[i+1],&a[r]);
}
return i+1;
}
void quicksort(int a[],int p,int r)
{
if(p<r)
{
int q;
q=partition(a,p,r);
quicksort(a,p,q);
quicksort(a,q+1,r);
}
}
main()
{
int a[50],i,size;
printf("enter the size of the array\n");
scanf("%d",&size);
printf("enter the elements of the array\n");
for(i=0;i<size;i++)
{
scanf("%d",&a[i]);
}
quicksort(a,0,size-1);
printa(a,size);
}
I'm trying to create a simple(?) selection sort program in C that selects the largest integer of an integer array and places it in the location a[n-1], places the second largest number in a[n-2], etc until the smallest number is placed in a[0]. I've run through the below code on paper and it seems like it should work, but when I compile it I'm getting faulty results. Am I missing something obvious?
/* The program implements selection sort*/
#include <stdio.h>
#include "simpio.h"
#define n 5
void GetArray(int a[]);
void SelectionSort(int a[]);
int FindMax(int a[], int high);
void swap(int a[], int p1, int p2);
void PrintArray(int a[]);
main()
{
int a[n];
GetArray(a);
SelectionSort(a);
PrintArray(a);
getchar();
}
void GetArray(int a[])
{
int i;
for(i=0;i<n;i++)
{
printf("Enter integer# %d", i+1);
a[i]=GetInteger();
}
}
void SelectionSort(int a[])
{
int i, max;
for(i=0;i<n;i++)
{
max=FindMax(a,i);
swap(a,max,(n-1-i));
}
}
int FindMax(int a[], int high)
{
int i, index;
index=high;
for(i=high;i<n;i++)
{
if(a[i]>a[index])
index=i;
}
return index;
}
void swap(int a[], int p1, int p2)
{
int temp;
temp=a[p2];
a[p2]=a[p1];
a[p1]=temp;
}
void PrintArray(int a[])
{
int i;
for(i=0;i<n;i++)
printf("a[%d]=%d\n", i, a[i]);
}
Change these method to:
void SelectionSort(int a[])
{
int i, max;
for(i=0;i<n;i++)
{
max=FindMax(a,n-i-1);
swap(a,max,n-i-1);
}
}
int FindMax(int a[], int high)
{
int i, index;
index=high;
for(i=0;i<high;i++)
{
if(a[i]>a[index])
index=i;
}
return index;
}
I actually tested my answer and it works.
Selection sort is process of comparing minimum element from the list and placing from the least index.
Now consider below code snippet.
public void selectionSort(int[] elements) {
for(int i=0;i<elements.length;i++) {
int minPosition = i;
for(int j=i+1;j<elements.length;j++) {
if(elements[minPosition]>elements[j])
minPosition = j;
}
int temp = elements[i];
elements[i] = elements[minPosition];
elements[minPosition] = temp;
}
}
Thanks for reading, let me know feedback to improve from myside
Shouldn't:
max=FindMax(a,i);
swap(a,max,(n-1-i));
Be:
max=FindMax(a,i);
swap(a,max,i);
otherwise, next time through the loop, you'll find the same max value in the top position in the array.
A very basic implementation of selection sort
#include<stdio.h>
main()
{
int i,j,n=7,a[]={1,2,5,3,8,9,5},key;
for(j=1;j<n;j++)
{
key=a[j]; //a[j] is the new element to be added to the sorted
//sequence
i=j-1;
while(i>=0 && key<a[i]) //traverse through the sorted sequence
{a[i+1]=a[i];i--;} //until the place of key is found
a[i+1]=key;
}
for (j=0;j<n;j++)
printf("%d",a[j]);
}
#include<stdio.h>
#include<conio.h>
int removex(int arr[],int small,int n)
{
int i=0;
for(;i<n;i++)
if(arr[i]==small) //searching that no to delete
break;
for(;i<n-1;i++)
arr[i]=arr[i+1]; //delete by overloading no
return n-1;
}
void selectSort(int arr[],int sort[],int n)
{
int j=0,k=0,small;
while(n!=0)
{
small=arr[0];
for(j=0;j<n;j++)
if(arr[j]<small)
small=arr[j]; //finding smallest no
sort[k++]=small;
n=removex(arr,small,n); //removing that from list as we included that no into sorted list
}
}
void main()
{
int arr[10],arr2[10],i,n;
clrscr();
printf("Enter how many elements");
scanf("%d",&n);
for(i=0;i<n;i++)
scanf("%d",&arr[i]);
selectSort(arr,arr2,n);
printf("sorted list is\n");
for(i=0;i<n;i++)
printf("%d\n",arr2[i]);
getch();
}