I got an assignment - creating an array and finding the index of maximum element in the array.
I need to do it with Log(N) run-time so I made a binary tree function, which right know returns the value of maximum element.
I am trying to change to so it can return the index of the maximum element with no luck so far.
appreciate any kind of help.
the code is :
void max_value(int *a, int i, int n)
{
int j, temp;
temp = a[i];
j = 2 * i;
while (j <= n)
{
if (j < n && a[j + 1] > a[j])
j = j + 1;
if (temp > a[j])
break;
else if (temp <= a[j])
{
a[j / 2] = a[j];
j = 2 * j;
}
}
a[j / 2] = temp;
return;
}
int Array_Search(int *a, int n) {
int i;
for (i = n / 2; i >= 1; i--)
{
max_value(a, i, n);
}
return a[1];
}
Related
I'm stuck with trying to get the number of searches done within a Binary search algorithm.
The goal is to test how many searches are done depending on how much data is put into the algorithm.
The program in question
//CBinarysearch.c//
#include <stdio.h>
#include <time.h>
#define NUM 100
#define MAX 200
int binary_s(int a[], int n, int s) {
int lo, hi, mid;
int c = 0;
lo = 0;//loの初期化
hi = n-1;//hiの初期化
while (lo <= hi) {
mid = (lo + hi) / 2;//midの初期化
c++;
if (s == a[mid]) break;//探索値がmidと同じ値となればloopを終了
if (s > a[mid])//探索値がmidより大きい場合
lo = mid + 1;//loの値を；１してmidへ移動
else//探索値がmidより小さい場合
hi = mid - 1;//hiの値をー１してmidへ移動
}
if (lo <= hi)
printf("The numerical value %d is in array %d (array element %d)\n", s, mid+1, mid);
else
printf("Could not be located.\n");
return c;
}
void shuffle(int a[]) {
unsigned int i, j;
int tmp;
i = MAX - 1;
while (i > 0) {//シャッフルのためのLoop
j = rand() % (i + 1);//jの値をランダム化
tmp = a[j];
a[j] = a[i];
a[i] = tmp;
i--;
}
}
int quicksort(int a[], int first, int last) {
int i, j, temp, x;
i = first;
j = last;
x = (a[i] + a[j]) / 2;//基準値は平均
while (1) {
while (a[i] < x) i++;
while (a[j] > x) j--;
//iがjより大きくなればwhile loopが解除される
if (i >= j) break;
//a[i]とa[j]を入れ替える
temp = a[i];
a[i] = a[j];
a[j] = temp;
i++;
j--;
}
if (first < i-1) quicksort(a, first, i-1);
if (j + 1 < last) quicksort(a, j + 1, last);
return 0;
}
int main(void) {
int a[NUM];
int i;
int count;
int s;
srand((unsigned int)time(NULL));
i = rand() % NUM;
s = a[i];
for (i = 0; i < NUM; i++) {//整列数列の作成
a[i] = i + 1;
}
shuffle(a);//Fisher-Yates shuffle
quicksort(a, 0, NUM-1);//クイックソートの呼び出し
count = binary_s(a, NUM, s);
printf("\n%d ", count);//交換回数の出力
return 0;
}
I've been at this for an embarrassingly long time. And at this point I am adding more details just to make this post viable. It's been rough.
May I ask for some help, please?
You intialize s as s = a[i]; before initializing the array: this has undefined behavior. You should instead write:
s = rand() % NUM + 1;
Furthermore the shuffle function assumes the array has MAX elements whereas you define it with a length of NUM in main(). You should pass the length to shuffle().
Also note that x = (a[i] + a[j]) / 2 would have undefined behavior if the values in the array can be arbitrary large.
You should also consider adding some white space between the code and the comments to make the code more readable, especially to non Japanese readers.
Here is a modified version:
//CBinarysearch.c//
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define NUM 100
int binary_s(int a[], int n, int s) {
int lo, hi, mid;
int c = 0;
lo = 0; // loの初期化
hi = n - 1; // hiの初期化
while (lo <= hi) {
mid = lo + (hi - lo) / 2; // midの初期化
c++;
if (s == a[mid]) // 探索€¤がmidと同じ€¤となればloopを終了
break;
if (s > a[mid]) // 探索€¤がmidより大きい場合
lo = mid + 1; // loの€¤を；１してmidへ移動
else // 探索€¤がmidより小さい場合
hi = mid - 1; // hiの€¤をー１してmidへ移動
}
if (lo <= hi) {
printf("The numerical value %d is in array at index %d\n",
s, lo);
} else {
printf("value %d Could not be located in array.\n", s);
}
return c;
}
void shuffle(int a[], int len) {
int i, j;
int tmp;
for (i = len - 1; i > 0; i--) { // シャッフルのためのLoop
j = rand() % (i + 1); // jの€¤をラン€ム化
tmp = a[j];
a[j] = a[i];
a[i] = tmp;
}
}
void quicksort(int a[], int first, int last) {
int i, j, temp, x;
if (first >= last)
return;
i = first;
j = last;
x = ((long long)a[i] + a[j]) / 2; // 基準€¤は平均
while (1) {
while (a[i] < x) i++;
while (a[j] > x) j--;
//iがjより大きくなればwhile loopが解除される
if (i >= j) break;
//a[i]とa[j]を入れ替える
temp = a[i];
a[i] = a[j];
a[j] = temp;
i++;
j--;
}
quicksort(a, first, i - 1);
quicksort(a, j + 1, last);
}
int main(void) {
int a[NUM];
int i;
int count;
int s;
srand((unsigned int)time(NULL));
for (i = 0; i < NUM; i++) { // 整列数列の作成
a[i] = i + 1;
}
s = a[rand() % NUM];
shuffle(a, NUM); // Fisher-Yates shuffle
quicksort(a, 0, NUM - 1); // クイックソートの呼び出し
count = binary_s(a, NUM, s);
printf("iterations: %d\n", count); // 交換回数の出力
return 0;
}
I'm new to programming,I'm trying to implement a merge sort function into my program, but it's not working correctly. I went over and over the code but I can't find the problem.
If for example the user input for a 6 element array is : 3 2 4 1 6 7
The output is: 1 3 2 4 32708 32708
Can someone help me? Also, if anyone have any advice for improving my coding style would be much appreciated.Thanks.
#include <stdio.h>
#include <stdlib.h>
int main(void) {
int *a, n;
a = malloc(100 * sizeof(int)); // dynamically allocating memory for original array
if (a == NULL)
return 1;
printf("Enter n of elements in the array:");
scanf("%i", &n); // n of elements the in array
printf("Enter elements:\n");
for (int i = 0; i < n; i++) {
scanf("%i", &a[i]); // prompt user for input elements
}
int f, l, m, n1, n2; // declaring variables
f = 0; // first element
l = n - 1; // last element
m = (f + l) / 2; // mid point
n1 = m + 1 - f; // n elements l1
n2 = l - m; // n elements l2
int l1[n1]; // temp array 1
int l2[n2]; // temp array2
for (int i = 0; i < n1; i++) {
l1[i] = a[i]; // copy elements into temp l1
}
for (int j = 0; j < n2; j++) {
l2[j] = a[m + 1 + j]; // copy elements into temp l2
}
int i, j, k; // variable for arrays index
i = 0;
j = 0;
k = 0;
//sorting and copying elements in original array
while (i < n1 && j < n2) {
if (l1[i] <= l2[j]) { // if element l1 smaller or equal to l2 element
a[k] = l1[i]; // copy element l1 into original array
i++; // increment l1
} else { // if element l1 bigger than l2
a[k] = l2[j]; // copy element l2 into original array
j++; // increment l2
}
k++; // increment original array
}
// copy remaining elements (if any)
while (i < n1) {
a[k] = l1[i];
i++;
k++;
}
while (j < n2) {
a[k] = l2[i];
j++;
k++;
}
printf("Your sorted array:\n");
for (int d = 0; d < n; d++) {
printf("%i ", a[d]); // print sorted array
}
printf("\n");
free(a); // freeing original array
}
You need to merge recursively. You wrote only the merge part and not the recursive sort function.
More info: https://www.geeksforgeeks.org/merge-sort/
#include <stdio.h>
#include <stdlib.h>
void merge(int arr[], int l, int m, int r)
{
int i, j, k;
int n1 = m - l + 1;
int n2 = r - m;
/* create temp arrays */
int L[n1], R[n2];
/* Copy data to temp arrays L[] and R[] */
for (i = 0; i < n1; i++)
L[i] = arr[l + i];
for (j = 0; j < n2; j++)
R[j] = arr[m + 1 + j];
/* Merge the temp arrays back into arr[l..r]*/
i = 0; // Initial index of first subarray
j = 0; // Initial index of second subarray
k = l; // Initial index of merged subarray
while (i < n1 && j < n2) {
if (L[i] <= R[j]) {
arr[k] = L[i];
i++;
} else {
arr[k] = R[j];
j++;
}
k++;
}
/* Copy the remaining elements of L[], if there are any */
while (i < n1) {
arr[k] = L[i];
i++;
k++;
}
/* Copy the remaining elements of R[], if there are any */
while (j < n2) {
arr[k] = R[j];
j++;
k++;
}
}
void mergeSort(int arr[], int l, int r)
{
if (l < r) {
// Same as (l+r)/2, but avoids overflow for
// large l and h
int m = l + (r - l) / 2;
// Sort first and second halves
mergeSort(arr, l, m);
mergeSort(arr, m + 1, r);
merge(arr, l, m, r);
}
}
int main(void)
{
int *a, n;
printf("Enter n of elements in the array:");
scanf("%i", &n); //n of elements the in array
a = malloc(n * sizeof(int)); //dynamically allocating memory for original array
if (a == NULL)
return 1;
printf("Enter elements:\n");
for (int i = 0; i < n; i++) {
scanf("%i", &a[i]); //prompt user for input elements
}
mergeSort(a, 0, n - 1);
printf("Your sorted array:\n");
for (int d = 0; d < n; d++) {
printf("%i ", a[d]); //print sorted array
}
printf("\n");
free(a); //freeing original array
return 0;
}
So that's my task. I don't know how to realize it in 2D.
All variables (i, j, L, R, etc. are integer)
while (L < R)
{
for(i, j = L; i < R; i++, j++)
{
if (a[i][j] > a[i + 1][j + 1])
{
temp = a[i][j];
a[i][j] = a[i + 1][j + 1];
a[i + 1][j + 1] = temp;
k = i;
}
}
R = k;
for(i, j = R - 1; i >= L; i--, j--)
{
if(a[i][j] > a[i + 1][j + 1])
{
temp = a[i][j];
a[i][j] = a[i + 1][j + 1];
a[i + 1][j + 1] = temp;
k = i;
}
}
L = k + 1;
}
I tried this code but I think that something is wrong with that.
Input:
1 10 5
4 0 8
8 18 3
Output: (That should be)
0 10 5
4 1 8
8 18 3
But current Output is
1 10 5
4 0 8
8 18 3
A function to swap values using call by reference.
void swap(int *a, int *b)
{
int temp;
temp = *a;
*a = *b;
*b = temp;
}
A function implementing shaker sort
void ShakerSort(int a[], int n)
{
int i, j, k;
for(i = 0; i < n;)
{
// First phase for ascending highest value to the highest unsorted index.
for(j = i+1; j < n; j++)
{
if(a[j] < a[j-1])
swap(&a[j], &a[j-1]);
}
// Decrementing highest index.
n--;
// Second phase for descending lowest value to the lowest unsorted index.
for(k = n-1; k > i; k--)
{
if(a[k] < a[k-1])
swap(&a[k], &a[k-1]);
}
// Incrementing lowest index.
i++;
}
}
The main function looks like this
int main()
{
int n, i;
cout<<"\nEnter the number of data element to be sorted: ";
cin>>n;
int arr[n];
for(i = 0; i < n; i++)
{
cout<<"Enter element "<<i+1<<": ";
cin>>arr[i];
}
ShakerSort(arr, n);
// Printing the sorted data.
cout<<"\nSorted Data ";
for (i = 0; i < n; i++)
cout<<"->"<<arr[i];
return 0;
}
The above code is written in c++ refer it and make the changes according to your requirment
I'm fairly new into programming and my teacher want me to implement insertion sort in C.
My code works, but not with negative numbers if I use it with negative numbers in my array I always get a segmentation fault:
void insertion_sort(int array[], int len) {
int i = 0;
int j = 1;
signed int tmp = array[0];
for(i = 1; i < len; i++) {
tmp = array[i];
j = i - 1;
if(j >= 0){
while(tmp < array[j]) {
array[j + 1] = array[j];
j = j - 1;
}
}
array[j + 1] = tmp;
}
}
Change this code snippet
if(j >= 0){
while(tmp < array[j]) {
array[j + 1] = array[j];
j = j - 1;
}
}
to
while ( j >= 0 && tmp < array[j] ) {
array[j + 1] = array[j];
j = j - 1;
}
Take into account that there is no sense to initialize defined variables
int i = 0;
int j = 1;
signed int tmp = array[0];
because they are overwritten in the followed statements.
I am trying to implement the merge sort algorithm in C. I understand how the algorithm is supposed to work however I am encountering some difficulties with the implementation.
I understand that there are hundreds of examples and source code for it's implementation but I was hoping someone could help me understand why mine is not working correctly.
My code is below and after the code I explain what I have tried so far.
#include <stdio.h>
void merge(int a[], int L[], int R[],int nL, int nR) //nL and nR are the lengths of L[] and R[]
{
int i = 0 , j = 0, k = 0;
while(i<nL && j <nR)
{
if(L[i] <= R[j]){
a[k] = L[i];
i++;
}
else{
a[k] = R[j];
j++;
}
k++;
}
while(i < nL){
a[k] = L[i];
i++;
k++;
}
while(j < nR) {
a[k] = R[j];
j++;
k++;
}
}
void mergesort(int a[],int n) //n is the length of a[]
{
if(n < 2) return; //BASE CASE
int mid = n / 2;
int left[mid];
int right[n-mid];
for(int i = 0; i < mid; i++)
{
left[i] = a[i];
}
for(int i = mid; i < n-1; i++)
{
right[i-mid] = a[i];
}
int nL = sizeof(left) / sizeof(left[0]);
int nR = sizeof(right) / sizeof(right[0]);
mergesort(left, nL);
mergesort(right, nR);
merge(a,left,right,nL,nR);
}
int main(void)
{
printf("Initial:\n");
printf("3 4 1 6\n");
int numbers[4] = {3,4,1,6};
int n = sizeof(numbers) / sizeof(int);
mergesort(numbers,n);
printf("Sorted:\n");
for(int i =0 ; i < 4; i++)
{
printf("%d ", numbers[i]);
}
return 0;
}
As it is and with the unsorted array [3,4,1,6] the output is 0 0 1 3.
Clearly the 1 and 3 are in the right order relative to each other but the two zeros at the beginning are clearly wrong. At first it seemed to me that I was inserting 4 and 6 to the right and out of bounds of the array.
I used some print statements to try and debug but I haven't been able to figure out what was going on. I even tried to follow my code with gdb but I still could not sort it.
Does any one have any ideas of what might be happening?
A more nearly idiomatic way of writing the merge() code would be:
void merge(int a[], int L[], int R[],int nL, int nR)
{
int i = 0, j = 0, k = 0;
while (i < nL && j < nR)
{
if (L[i] <= R[j])
a[k++] = L[i++];
else
a[k++] = R[j++];
}
while (i < nL)
a[k++] = L[i++];
while (j < nR)
a[k++] = R[j++];
}
That's about half the number of lines of your code, and within broad limits, the less code there is to read, the better. There are those who insist on having braces after each loop or conditional. I don't think that's necessary (or particularly helpful), but if that's the style you like, you can use it.
Your mergesort() code is less flabby, but could be changed to:
void mergesort(int a[],int n) //n is the length of a[]
{
if (n < 2)
return; //BASE CASE
int mid = n / 2;
int left[mid];
int right[n-mid];
for (int i = 0; i < mid; i++)
left[i] = a[i];
for (int i = mid; i < n; i++)
right[i-mid] = a[i];
mergesort(left, mid);
mergesort(right, n - mid);
merge(a, left, right, mid, n - mid);
}
This includes the fix for your main problem — the loop loading the right array was leaving the last element uncopied.
With a debugging function such as:
void dump_array(const char *tag, int n, int *a)
{
printf("%s:%d:", tag, n);
for (int i = 0; i < n; i++)
printf(" %3d", a[i]);
putchar('\n');
}
You can do a lot of effective debugging with:
void mergesort(int a[],int n)
{
if (n < 2)
return;
int mid = n / 2;
int left[mid];
int right[n-mid];
dump_array("-->>mergesort()", n, a);
for (int i = 0; i < mid; i++)
left[i] = a[i];
dump_array("left", mid, left);
for (int i = mid; i < n; i++)
right[i-mid] = a[i];
dump_array("right", n - mid, right);
mergesort(left, mid);
dump_array("merged-L", mid, left);
mergesort(right, n - mid);
dump_array("merged-R", n - mid, right);
merge(a, left, right, mid, n - mid);
dump_array("<<--mergesort()", n, a);
}
In your code, the output with the tag right would show 0 or semi-random data for the last element, rather than what you're expecting. This would be a hint as to where the trouble is. Keep the dump_array() function around; it is a useful creature to have. It's a simple-minded version; you can invent more complex versions which outputs a newline at intermediate positions for long arrays, for example.
The issue is in the following code:
for(int i = mid; i < n-1; i++)
{
right[i-mid] = a[i];
}
It should be:
for(int i = mid; i < n; i++) // right should range from mid to n - 1 *inclusive*
{
right[i-mid] = a[i];
}
This is simple implementation of merge sort without any complications. Just pass the array pointer and total number of entires in the array.
void merge(int *a, int top)// Array pointer and max entries
{
int l1, k, l2, u1, u2, size = 1, i, j;
int *sa;
sa = (int *)calloc(top, sizeof(int));
while (size < top)
{
l1 = 0;
k = 0;
while (l1 + size < top)
{
l2 = l1 + size;
u1 = l2 - 1;
u2 = ((l2 + size - 1) < top ? l2 + size - 1 : top - 1);
for (i = l1, j = l2; i <= u1 && j <= u2; )// Merging
{
sa[k++] = a[i] <= a[j] ? a[i++] : a[j++];
}
for ( ; i <= u1; )
sa[k++] = a[i++];
for ( ; j <= u2; )
sa[k++] = a[j++];
l1 = u2 + 1;
}
for (i = l1; i < top; i++) // For the left outs of the process
sa[k++] = a[i];
for (i = 0; i < top; i++)
a[i] = sa[i];
size *= 2;
}
}