This is my implementation of BFS in C
void bfs(int* vertices, Edge* edges, int num_vertices, int num_edges){
int level = 0;
int modified;
//continue looping till all vertices have not been updated
do{
modified = 1;
for (int i = 0; i < num_edges; ++i)
{
int first = edges[i].first;
int second = edges[i].second;
if ((vertices[first] == level) &&(vertices[second] == -1))
{
vertices[second] = level + 1;
modified = 0;
}else if (vertices[second]== level && (vertices[first] == -1))
{
vertices[first] = level + 1;
modified = 0;
}
}//end of for
level++;
}while(modified != 0);
}
The code is supposed to write the level of each vertex corresponsding to a starting vertex in a vetices array. The array is initialized using this function.
void initialize_vertices(int* vertices, int size, int start_vertex){
for (int i = 0; i < size; ++i)
{
if(i == start_vertex){
vertices[i] = 0;
}else{
vertices[i] = -1;
}
}
}
An edge is defined as follows
typedef struct Edge{
int first;
int second;
}Edge;
This is my calling main function.
int main(int argc, char** argv){
const int NUM_VERTICES = 128;
const int NUM_EDGES = 128;
const int START_VERTEX = 25;
clock_t begin, end;
double time_spent;
int vertices[NUM_VERTICES];
Edge edges[NUM_EDGES];
//data set
for (int i = 0; i < NUM_EDGES; ++i)
{
edges[i].first = (rand() % (NUM_VERTICES+1));
edges[i].second = (rand() % (NUM_VERTICES+1));
}
initialize_vertices(vertices, NUM_VERTICES, START_VERTEX);
begin = clock();
bfs(vertices, edges, NUM_VERTICES, NUM_EDGES);
end = clock();
time_spent = (double)(end - begin) / CLOCKS_PER_SEC;
printf("Time taken: %f\n", time_spent);
for (int i = 0; i < NUM_VERTICES; ++i)
{
printf("%d : %d", i, vertices[i]);
printf(((i % 4) != 3) ? "\t":"\n");
}
return 0;
}
The issue is that the code never terminates. What am I doing wrong, any help appreciated.
Your modified logic is flawed.
By default, you are setting modified to 1, which I guess means that something has been modified.
Then
}while(modified != 0);
correctly loops if anything has been modified.
You want to initially set modified to 0 and change it to 1 in the inner if.
Yo reenter the loop if you don't modify anything. That seems to be your problem.
You set modified = 1 at the beginning of your loop and only change that to 0 if something changed. When you ask in the end modified != 0 it will return true if and only if there was no change.
Related
It's been a few hours and i can't seem to understand the issue. Build this program to count from 1 - 10. The goal of this program is to use multithreading and dynamically split the array depending on how many threads it requested. Problem is the first 2 threads are being skipped and the last thread is doing most of th e process. I suspect it's the for loop that creates the threads.
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
typedef struct
{
int *array;
int batch;
int start;
int end;
} Parameter;
void *method(void *p)
{
Parameter *param = (Parameter *)p;
for (int i = param->start; i < param->end; i++)
{
printf("Start:%d\tEnd:%d\tIndex:%d\tValue:%d\n", param->start, param->end, i,param->array[i]);
}
}
int main(int argc, char **argv)
{
// Getting the user input
int array_length = atoi(argv[1]);
int batches = atoi(argv[2]);
printf("User specified Array:%d\tBatch:%d\n", array_length, batches);
// Creating an array
int *array = (int *)calloc(array_length, sizeof(int));
// Fill it up with some data
for (int i = 0; i < array_length; i++)
{
array[i] = i;
}
// Determine the Batches
int batch_size = array_length / batches;
int remainder = array_length % batches;
printf("%d\n", batch_size);
printf("%d\n", remainder);
int start = 0;
int end = 0;
int index =0;
// List of parameters
Parameter *param = (Parameter *)calloc(batches, sizeof(Parameter));
pthread_t *threads = (pthread_t *)calloc(batches, sizeof(pthread_t));
// Loop through each batch.
for (int i = 0; i < batches; i++)
{
printf("\n\nBatch number -> %d\n", i);
end = start + batch_size;
if (remainder > 0)
{
remainder --;
end ++;
}
// Fill the parameters
param[i].array = array;
param[i].end = end;
param[i].start = start;
param[i].batch = i;
// Call the thread.
pthread_create(threads + index, NULL, method, (void *)¶m[i]);
index++;
start = end;
}
for (int i = 0; i < batches; i++)
{
pthread_join(threads[i], NULL);
}
free(param);
free(threads);
free(array);
return 0;
}
Been playing with the index of the for loop(line 57) as i'm certain it's the cause of the issue. been getting some results but the main problem still persisted.
Code Works as intended. I'm a dumbas who didn't put the printf in the void function. like so:
void *method(void *p) {
Parameter *param = (Parameter *)p;
printf("\n\nBatch number -> %d\n", param->batch); //<-- moved from main method
for (int i = param->start; i < param->end; i++)
{
printf("Start:%d\tEnd:%d\tIndex:%d\tValue:%d\n", param->start, param->end, i,param->array[i]);
} }
Thanks for pointing it out that the program works
I want to changed the value of code_array in function HuffmanTree_code.
when I run the HuffmanTree_code(HuffmanTree T,char *code_array[M]),debug show the right result as image1,then I want to use the value of code_array,when I print the first char value of code_array for the first time ,the rest of code_array get garbled as image 2.Please help。
PS:if you want the whole program ,please tell me.
PSS:What I learn is the Huffman coding,if you have some solutions,please commit,please,please。
void HuffmanTree_code(HuffmanTree T,char *code_array[M])
{
char code[M] = {0,0,0};
char onecode[M];
char code_aa[N][M];
int length = 0;
int i = 0;
int j = 0;
int m = 0;
int t = 0;
int cop = 0;
for ( m = 0; m < N; m++)
{
j = M - 2;
i = m;
while (T[i].parent != 0)
{
if (T[T[i].parent].lchild == i)
code[j--] = '0';
else
code[j--] = '1';
i = T[i].parent;
}
length = M - 2 - j;
strcpy(onecode, code+j+1);
strcpy(code_aa[m], onecode);
code_array[m] = code_aa[m];
printf("%s\n", code_aa[m]);
}
}
int main()
{
//code
HuffmanTree_code(T1,code);
printf("%s\n", code[0]);
}
Debug image:
run the HuffmanTree_code(T1,code);
run the printf("%s\n", code[0])
Code:
#include <stdio.h>
void testSort(int values[], int n);
int main(void)
{
int hs[] = {5,3,2,1,4};
printf("Unsorted: %i %i %i %i %i\n", hs[0], hs[1], hs[2], hs[3], hs[4]);
testSort(hs, 5);
printf("Sorted: %i %i %i %i %i\n", hs[0], hs[1], hs[2], hs[3], hs[4]);
}
void testSort(int values[], int n)
{
for (int i = 0; i < n-1; i++)
{
int hold;
int current = values[i];
int next = values[i + 1];
if (current > next)
{
hold = current;
current = next;
next = hold;
}
}
return;
}
I'm trying to do bubble sort and right now it goes through the array once, but my question is: Why isn't my hs[] updating after calling function? The second printf shows that it remained the same.
EDIT:
As mentioned, turns out I was changing data but of the copies. For some reason I when I created the variables current/next I felt as if they were representing values[i]/values[i+1] but in reality I was just creating new variable and passing the value of values[0] which is 5 and assigning it to current. Obviously leaving values[] unchanged. Thanks everyone
The problem is that you're only modifying the function's local variables, not the array's elements.
It's the same principle as why this program will print 1 and not 2:
int main()
{
int array[] = {1};
int x = array[0];
x = 2;
printf("array[0] = %d\n", array[0]);
return 0;
}
You need to assign values to the array's elements:
void testSort(int values[], int n)
{
for (int i = 0; i < n-1; i++)
{
if (values[i] > values[i+1])
{
int hold = values[i];
values[i] = values[i+1];
values[i+1] = hold;
}
}
}
Once you've fixed this, you will notice that this function only works for some inputs.
Solving that bug is left as an exercise.
Please try below code:-
void bubble_sort(int list[], int n){
int c, d, t;
for (c = 0 ; c < ( n - 1 ); c++)
{
for (d = 0 ; d < n - c - 1; d++)
{
if (list[d] > list[d+1])
{
t = list[d];
list[d] = list[d+1];
list[d+1] = t;
}
}
}
}
Hi Guys i have edited the questions.Here is my entire code.I have given basic amount of readability to my program.I hope u guys can understand the program.
#include<stdio.h>
#include<stdlib.h>
int Max_Min(int,int,int,int *, int *);
int *Max,Number;
int main()
{
int n1, n2,Maximum_Element=0,*Max;
int i = 0, j = 0;
scanf("%d",&Number);
Max =(int *) malloc(sizeof(int)*Number);//Array Max is created
for (int k = 0;k <(Number/2);k++)
{
scanf("%d", &n1);
scanf("%d", &n2);
Max[k] = Max_Min(0,1,0,&n1,&n2);//Passing integer elements n1,n2 with flag 0
}
Maximum_Element=Max_Min(1,1,((sizeof(Max)*Number)/8),Max,Min);//Passing array elements Max,Min with flag 1 to function Max_Min
printf("Maximum_Element=%d", Maximum_Element);
return 0;
}
int Max_Min(int flag,int Max_Min_flag,int length,int *n1,int *n2)//n1 and n2 should be able to handle array and integers
{
int i=0,j = 0,k1,k2,Min1 = 0, Min2 = 0,count=0, Not_Zero = 0,x=0,y=0, *New_Max = 0,*New_Min;
/*Recursive Loop for splitting the array elements and calling the array */
if (flag == 1)
{
New_Max = (int *)(malloc(sizeof(int)*length));
for (;i <= ((length) / 2);i = i + 2)//
{
k1 = n1[i];
j = i + 1;
if (j <= ((length + 1) / 2))
{
k2 = n1[j];
New_Max[count] = Max_Min(0, 1, 0, &k1, &k2);//It is passing integer elements with flag 0 to function Max_Min
count++;
}
}
New_Max[count] = n1[j + 1];
for (int i = 0;i < count + 1;i++)
{
**/* Problem is assigning Max[i]=New_Max[i] is not getting assigned*/**
Max[i] = New_Max[i];//Copying from New_Max to Max because New_Max will be overwritten,so possible chaunce of dataloss
Not_Zero++;
}
while ((sizeof(Max) / 4 - (Not_Zero))>0)
{
Max[Not_Zero] = 0;
Not_Zero++;
}
/*Logic for calling recursive functions based on the count*/
if (count > 1)
{
count--;
Max_Min(1, 1, count, Max, Min);//Calling Recursive function by Passing Entire Arrays with flag 1.
}
else if (count == 1 && Max[1] == 0)
{
*n1 = Max[0];
*n2 = Min[0];
}
else if (count == 1 && Max[2] == 0)
{
Max_Min(1, 1, count + 1, Max, Min);
count--;
}
}
/*Logic for Finding Maximum & Minimum element is present down*/
if (flag == 0)
{
printf("flag");
if (Max_Min_flag == 1)
{
if (*n1 > *n2)
{
}
else if ((*n1 < *n2) && Max_Min_flag == 1)
{
int temp = 0;
temp = *n1;//5
*n1 = *n2;//7
*n2 = temp;//5
}
}
else if (Max_Min_flag == 2)
{
if (*n1 > *n2)//7>2
{
int temp = 0;
temp = *n1;//2
*n1 = *n2;//2
*n2 = temp;//2,7
}
else if (*n1 < *n2)
{
}
}
}
return *n1;//7
}
Problem is assigning Max[i]=New_Max[i] in function Max_Min().It shows Run time error as "Access violation writing location 0x00000000."
First you need to #include <stdlib.h> to use malloc
You must declare your function before using it.
func must return int*.
Also in func "n", first "Max", and second "Max" needs to be the same variable. Rename "n" to "Max"
This is the code corrected with an extra printf;
#include <stdio.h>
#include <stdlib.h>
int *Max,Number=5;
int* func(int *Max)
{
for(int j=0;j<5;j++)
Max[j]=j;//Its not working in this line
return Max;
}
int main()
{
Max=(int *) malloc(sizeof(int)*Number);
for(int i=0;i<5;i++)
Max[i]=i;
int* x = func(Max);
for(int i=0;i<5;i++)
printf("%d", x[i]);
}
The following contains only minor adaptations of your code and it runs fine:
int *func(int *n);
int *Max,Number=5;
int main()
{
int *x,i;
Max=(int *) malloc(sizeof(int)*Number);
for(i=0;i<Number;i++)
Max[i]=i;
x=func(Max);
free(Max);
return(0);
}
int *func(int *n)
{
int j;
for (j=0;j<Number;j++)
n[j]=Number-j; // reverse the number, just to check
return Max;
}
I'm working on a C implementation as an exercise (I'm a student). I have the logic fine (I've used the implementation itself before), but I get a segfault when actually running it. I've looked for a long time, and I can't understand what's causing it. Here is my complete code:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define ARRAY_CAPACITY 50
void do_sort(int* list);
void merge_sort(int* list_of, int* buffer_of, int start, int end);
void do_sort(int* list)
{
int capacity = ((ARRAY_CAPACITY) / 2);
int buffer[capacity];
merge_sort(list, buffer, 0, ARRAY_CAPACITY);
}
void merge_sort(int* list_of, int* buffer_of, int start, int end)
{
printf("%s", "hi!");
int i, t;
if((end - start) < 2) return;
int mid = (start + end) / 2;
merge_sort(list_of, buffer_of, start, mid);
merge_sort(list_of, buffer_of, mid, end);
int left = 0;
int right = mid;
for(i = 0; i < ARRAY_CAPACITY; i++)
{
buffer_of[i] = list_of[i];
}
for(t = start; t < end; t++)
{
if((left < (mid - start)) && (right == end || buffer_of[left] < list_of[right]))
{
list_of[t] = buffer_of[left];
left++;
}
else
{
list_of[t] = list_of[right];
right++;
}
}
}
int main()
{
srand(time(NULL));
int number_array[ARRAY_CAPACITY];
int i;
for(i = 0; i < ARRAY_CAPACITY; i++)
{
number_array[i] = (rand() % 100);
}
printf("%d\n", number_array[3]);
int j, m;
printf("%s\n", "Pre-Sorted Array: ");
for(j = 0; j < ARRAY_CAPACITY; j++)
{
printf("%d ", number_array[j]);
}
do_sort(number_array);
for(m = 0; m < ARRAY_CAPACITY; m++)
{
printf("%d ", number_array[m]);
}
printf("\n");
}
The output is as follows:
50 (this is a random number, but it always prints successfully)
Pre-Sorted Array:
Segmentation fault
So the segfault triggers when I try to loop to print the pre sorted array, but I've just proven that the array values were properly set, so I can't fathom this error. Help?
You have the following code:
void merge_sort(int* list_of, int* buffer_of, int start, int end)
{
...
for(i = 0; i < ARRAY_CAPACITY; i++)
{
buffer_of[i] = list_of[i];
}
...
That code will get called, at one point, with the following arguments:
list_of is an array of 50 integers.
buffer_of is an array of 25 integers.
start is 0.
end is 50.
You will copy 50 elements of list_of into buffer_of, but buffer_of has only room for 25 elements.