I have written a simple recursion procedure for DFS.
#include <stdbool.h>
void mydfs(int ROWS, int COLS,char **A,int row, int col, bool **visited){
static int rowAdjacencyParams[4] = {-1,0,1,0};
static int colAdjacencyParams[4] = {0,1,0,-1};
*(*(visited+col)+row) = true;
//visited[row][col] = true;
int i,newR,newC;
for(i = 0;i<4;i++){
newR = row + rowAdjacencyParams[i];
newC = col + colAdjacencyParams[i];
if(((newR >=0) && (newR < ROWS)) && ((newC>=0) && (newC < COLS))){
/*if((A[newR][newC] == 'X') && !visited[newR][newC]){
mydfs(ROWS,COLS,A,newR,newC,visited);
}*/
}
}
}
int black(char** A, int n1) {
int i,j,count = 0;
int cols = strlen(A[0]);
bool visited[n1][cols];
memset(visited,0,sizeof(visited));
for(i = 0;i<n1;i++){
for(j = 0;j<cols;j++){
if((A[i][j] == 'X') && !visited[i][j]){
count++;
mydfs(n1,cols,A,i,j,visited);
}
}
}
return count;
}
int main(){
int ROWS = 3;
int COLS = 7;
char P[ROWS][COLS]= {"OOOXOOO","OOXXOXO","OXOOOXO"};
printf("Number of islands = %d",black(P,COLS));
return 0;
}
UPDATED main Function
However, when I run this it gives me a segmentation fault for line visited[row][col] = true;. Then I tried to change it to *(*(visited+col)+row) = true; but still having the same segmentation fault error. Please explain why am I getting this error.
In addition to the character data exceeding the array's buffer as pointed out by the comments, beyond that another error is this:
int black(char** A, int n1) {
//...
for(i = 0;i<n1;i++){
for(j = 0;j<cols;j++){
if((A[i][j] == 'X') && !visited[i][j]){ /* A[i] is out of bounds */
The n1 is passed in as the number of columns, which is 7. However if you go back to main, you have this:
int ROWS = 3;
int COLS = 7;
char P[ROWS][COLS]= {"OOOXOOO","OOXXOXO","OXOOOXO"};
printf("Number of islands = %d",black(P,COLS));
The P array has only 3 rows. So when the black function is called, it is assuming that P has 7 rows, not 3 rows. This results in the A array accessing A[0], A[1], A[2], (good), but then A[3], etc. which is undefined behavior (and in your case, a crash).
So you need to get your column / row logic corrected.
I will let you in on a secret. Since you originally tagged your question as C++, I took the time to change those double stars to std::vector, and use the at() function to locate the issue. I know that you've now tagged your question as C99, but I would just like to be aware why tags are important. I don't know if C99 has this feature of auto-detecting boundary conditions like this.
Related
This is a classic question, where a list of coin amounts are given in coins[], len = length of coins[] array, and we try to find minimum amount of coins needed to get the target.
The coins array is sorted in ascending order
NOTE: I am trying to optimize the efficiency. Obviously I can run a for loop through the coins array and add the target%coins[i] together, but this will be erroneous when I have for example coins[] = {1,3,4} and target = 6, the for loop method would give 3, which is 1,1,4, but the optimal solution is 2, which is 3,3.
I haven't learned matrices and multi-dimensional array yet, are there ways to do this problem without them? I wrote a function, but it seems to be running in an infinity loop.
int find_min(const int coins[], int len, int target) {
int i;
int min = target;
int curr;
for (i = 0; i < len; i++) {
if (target == 0) {
return 0;
}
if (coins[i] <= target) {
curr = 1 + find_min(coins, len, target - coins[i]);
if (curr < min) {
min = curr;
}
}
}
return min;
}
I can suggest you this reading,
https://www.geeksforgeeks.org/generate-a-combination-of-minimum-coins-that-results-to-a-given-value/
the only thing is that there is no C version of the code, but if really need it you can do the porting by yourself.
Since no one gives a good answer, and that I figured it out myself. I might as well post an answer.
I add an array called lp, which is initialized in main,
int lp[4096];
int i;
for (i = 0; i <= COINS_MAX_TARGET; i++) {
lp[i] = -1;
}
every index of lp is equal to -1.
int find_min(int tar, const int coins[], int len, int lp[])
{
// Base case
if (tar == 0) {
lp[0] = 0;
return 0;
}
if (lp[tar] != -1) {
return lp[tar];
}
// Initialize result
int result = COINS_MAX_TARGET;
// Try every coin that is smaller than tar
for (int i = 0; i < len; i++) {
if (coins[i] <= tar) {
int x = find_min(tar - coins[i], coins, len, lp);
if (x != COINS_MAX_TARGET)
result = ((result > (1 + x)) ? (1+x) : result);
}
}
lp[tar] = result;
return result;
}
I am trying to find unique non-zero intersection between two sets. I have written a program which works for some set of arrays but gives segmentation fault for some. I have been trying to figure out why but have failed, any help will be greatly valued. The thing is the functions defined (NoRep and ComEle) are working fine but are unable to return the value to the assigned pointer in the case when Seg Fault is shown. Below is the code:
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
int* ComEle(int ar_1[], int size_ar1, int ar_2[], int size_ar2);
int* NoRep(int a[], int l1);
int main ()
{
// Case 1: Gives segmentation fault
int A[10] = {1,1,0,2,2,0,1,1,1,0};
int B[10] = {1,1,1,1,0,1,1,0,4,0};
int *C = ComEle(A,10,B,10); printf("check complete\n");
// //Case 2: Does not give segmentation fault
// int A[4] = {2,3,4,5};
// int B[4] = {1,2,3,4};
// int *C = ComEle(A,4,B,4); printf("check complete\n");
}
//---------------- Local Functions --------------------//
int* ComEle(int ar_1[], int size_ar1, int ar_2[], int size_ar2) {
// sort of intersection of two arrays but only for nonzero elements.
int i=0, j=0, cnt1 = 0;
int temp1 = size_ar1+size_ar2;
int CE1[temp1]; for(i=0;i<temp1;i++) {CE1[i] = 0;}
/* Size of CE1 is knowingly made big enough to accommodate repeating
common elements which can expand the size of resultant array to
values bigger than those for the individual arrays themselves! */
for(i=0;i<size_ar1;i++) {
j = 0;
while(j<size_ar2) {
if(ar_1[i]==ar_2[j] && ar_1[i]!=0) {
CE1[cnt1] = ar_1[i];
cnt1++;
}
j++;
}
}
// Have to remove repeating elements.
int *CE = NoRep(CE1, cnt1);
for(i=0;i<(CE[0]+1);i++) {printf("CE:\t%d\n", CE[i]);}
printf("ComEle: %p\n",CE);
return(CE);
}
int* NoRep(int a[], int l1) {
int cnt = 0, i = 0, j =0;
int *NR; NR = (int*)calloc((l1), sizeof(int));
//int NR[l1]; for(i=0;i<l1;i++) {NR[i] = 0;}
for(i=0;i<l1;i++) {
j = 0;
while(j<i) {
if(a[i]==a[j]) {break;}
j++;
}
if(j == i) {
cnt++;
NR[cnt] = a[i];
}
}
NR[0] = cnt; // First element: # of relevant elements.
printf("NoRep: %p\n",NR);
return(NR);
}
Thanks again for your help!
Take a look at this code:
int temp1 = size_ar1+size_ar2;
int CE1[temp1]; for(i=0;i<temp1;i++) {CE1[i] = 0;}
/* Size of CE1 is knowingly made big enough to accommodate repeating
common elements which can expand the size of resultant array to
values bigger than those for the individual arrays themselves! */
for(i=0;i<size_ar1;i++) {
j = 0;
while(j<size_ar2) {
if(ar_1[i]==ar_2[j] && ar_1[i]!=0) {
CE1[cnt1] = ar_1[i];
cnt1++;
}
j++;
}
}
Here you have nested loops, i.e. a for-loop with a while-loop inside. So - in worst case - how many times can cnt1 be incremented?
The answer is size_ar1 * size_ar2
But your code only reserve size_ar1 + size_ar2 element for CE1. So you may end up writing outside the array.
You can see this very easy by printing cnt1 inside the loop.
In other words - your CE1 is too small. It should be:
int temp1 = size_ar1*size_ar2; // NOTICE: * instead of +
int CE1[temp1]; for(i=0;i<temp1;i++) {CE1[i] = 0;}
But be careful here - if the input arrays are big, the VLA gets huge and you may run in to stack overflow. Consider dynamic memory allocation instead of an array.
Besides the accepted answer: I have been missing a break statement in the while loop in ComEle function. It was not giving me the expected value of cnt1. The following will be the correct way to do it:
for(i=0;i<size_ar1;i++) {
j = 0;
while(j<size_ar2) {
if(ar_1[i]==ar_2[j] && ar_1[i]!=0) {
CE1[cnt1] = ar_1[i];
cnt1++;
break;
}
j++;
}
}
This will also do away with the requirement for a bigger array or dynamic allocation as suggested (and rightly so) by #4386427
I'm trying to understand how the return value of a function works, through the following program that has been given to me,
It goes like this :
Write a function that given an array of character v and its dim, return the capital letter that more often is followed by its next letter in the alphabetical order.
And the example goes like : if I have the string "B T M N M P S T M N" the function will return M (because two times is followed by N).
I thought the following thing to create the function:
I'm gonna consider the character inserted into the array like integer thank to the ASCII code so I'm gonna create an int function that returns an integer but I'm going to print like a char; that what I was hoping to do,
And I think I did, because with the string BTMNMPSTMN the function prints M, but for example with the string 'ABDPE' the function returns P; that's not what I wanted, because should return 'A'.
I think I'm misunderstanding something in my code or into the returning value of the functions.
Any help would be appreciated,
The code goes like this:
#include <stdio.h>
int maxvolte(char a[],int DIM) {
int trovato;
for(int j=0;j<DIM-1;j++) {
if (a[j]- a[j+1]==-1) {
trovato=a[j];
}
}
return trovato;
}
int main()
{
int dim;
scanf("%d",&dim);
char v[dim];
scanf("%s",v);
printf("%c",maxvolte(v,dim));
return 0;
}
P.S
I was unable to insert the value of the array using in a for scanf("%c,&v[i]) or getchar() because the program stops almost immediately due to the intepretation of '\n' a character, so I tried with strings, the result was achieved but I'd like to understand or at least have an example on how to store an array of character properly.
Any help or tip would be appreciated.
There are a few things, I think you did not get it right.
First you need to consider that there are multiple pairs of characters satisfying a[j] - a[j+1] == -1
.
Second you assume any input will generate a valid answer. That could be no such pair at all, for example, ACE as input.
Here is my fix based on your code and it does not address the second issue but you can take it as a starting point.
#include <stdio.h>
#include <assert.h>
int maxvolte(char a[],int DIM) {
int count[26] = {0};
for(int j=0;j<DIM-1;j++) {
if (a[j] - a[j+1]==-1) {
int index = a[j] - 'A'; // assume all input are valid, namely only A..Z letters are allowed
++count[index];
}
}
int max = -1;
int index = -1;
for (int i = 0; i < 26; ++i) {
if (count[i] > max) {
max = count[i];
index = i;
}
}
assert (max != -1);
return index + 'A';
}
int main()
{
int dim;
scanf("%d",&dim);
char v[dim];
scanf("%s",v);
printf("answer is %c\n",maxvolte(v,dim));
return 0;
}
#include <stdio.h>
int maxvolte(char a[],int DIM) {
int hold;
int freq;
int max =0 ;
int result;
int i,j;
for(int j=0; j<DIM; j++) {
hold = a[j];
freq = 0;
if(a[j]-a[j+1] == -1) {
freq++;
}
for(i=j+1; i<DIM-1; i++) { //search another couple
if(hold==a[i]) {
if(a[i]-a[i+1] == -1) {
freq++;
}
}
}
if(freq>max) {
result = hold;
max=freq;
}
}
return result;
}
int main()
{
char v[] = "ABDPE";
int dim = sizeof(v) / sizeof(v[0]);
printf("\nresult : %c", maxvolte(v,dim));
return 0;
}
I've been asked to write a code that takes 2, 1D arrays from a text file, add them and then return the results to another text file. Yet, I still get errors about pointers. I'm a C newbie and I'll be very happy if someone could explain it to me.
int result(int a[], int b[])
{
int *wsk = &c_tab[0];
char choice;
printf("0.Add\n1.Substract");
scanf("%c", &choice);
for (i=0; i<9; i++) {
if (choice== '0')
{
*wsk = a[i] + b[i];
wsk++;
}
else if (choice== '1')
{
*wsk = a[i] - b [i];
wsk++
}
}
return *wsk;
}
The first error I see is that you need to declare the function type with the type of the returned value, in this case the function has to be:
int *dzialanie(int a[], int b[]){
...
return wsk;
}
Another error is in the for loop, the operation has to be:
...
for (int i=0; i<9; i++){
*(wsk + i) = a[i] + b[i];
}
...
Same for the another (See that you didn't declare the i which is a variable too). Another way, is doing:
wsk[i] = a[i] - b[i];
Is the same.
If you already know the dimension of the two arrays, maybe is better to take the arguments as pointers, it will look like:
int dzialanie(int *a, int *b){
...
}
And you will have to allocate memory, this coul be done with malloc:
wsk = (int *)malloc(10*sizeof(int));
At the end of your program you will want to free that allocated memory, doing:
free(wsk);
Hope you understand, my english is poor, I'm from Argentina. Greetings!
since you are using a global variable the return type should be void(and or some form of indication that the calculation has been done. which in turn could be a simple return value of -1 or w/e(i'll leave that part up to you).
int res[10]; // global variable
void add(int *a, int *b) // no return value, new array will be saved globally(not advisable)
{
int sign = -1; // your +- check
printf("0.Suma\n1.Roznica");
scanf("%c", &sign);
if (sign == 0)
{
for (int i = 0; i < 9; i++)
res[i] = a[i] + b[i];
}
else if (sign == 1)
{
for (int i = 0; i < 9; i++)
res[i] = a[i] - b[i];
}
}
an alternative way of doing it would be to use either a or b as "return" values with a simple change like a[i] += b[i] -> now a has the value of a + b. this way you won't have to deal with pointers going out of scope etc(documentation of how to return pointers from functions(in a safe way) is here).
I recently joined Stackoverflow community because I had to ask this question. I've been searching for possible explanations and solutions on the website but so far nothing enlightened me as I wanted. My error is probably caused by a very specific line of code. I'm trying to create a function that reads an array of struct votes, (struct contains integer member number, char *category, char *nominee) and copies all the votes that contain the same number and category to another array of struct. Basically to show all the repeated votes.
typedef struct
{
int member;
char *categ;
char *nom;
}Vote
Vote vote(int member, char *categ, char *nom)
{
Vote result;
result.member = member;
result.categ = categ;
result.nom = nom;
return result;
}
int votes_count(Vote *v, int n, Vote *v1)
{
int result = 0;
int *index = malloc(sizeof(int) * 1000);
int a = 0;
for (int i = 0; i < n; ++i)
{
for (int j = 0; j < n; ++j)
{
if (a == 0 && v[i].member == v[j].member && strcmp(v[i].categ, v[j].categ) == 0)
{
v1[result++] = vote(v[j].member, str_dup(v[j].categ), str_dup(v[j].nom));
index[a++] = j;
}
for (int b = 0; b < a; ++b)
{
if( a > 0 && v[i].member == v[j].member && strcmp(v[i].categ, v[j].categ) == 0 && j != index[b])
{
v1[result++] = voto(v[j].member, str_dup(v[j].categ), str_dup(v[j].nom));
index[a++] = j;
}
}
}
}
return result;
}
Afterwads, it returns the number of elements of new array that contains all repetitions. I want to use an array of ints to save all line indexes so that the function doesn't read and copy the lines it already accounted.
Sorry if the code is hard to understand, if needed I can edit to be more understandable. Thanks for any answears.
P.S: I'm portuguese, sorry in advance for grammar mistakes
if your only intention is to harvest the duplicates, you only need to compare to the elements that came before an element
you don't need the index[] array
For simplicity, I used two integer arrays, you should change them to your struct arrays, also change the compare function.
unsigned fetchdups(int orig[], int dups[], unsigned count)
{
unsigned this, that, ndup=0;
for (this=1; this<count; this++){
for (that=0; that<this; that++){
/* change this to your compare() */
if(orig[that] == orig[this]) break;
}
if (this == that) continue; /* no duplicate */
dups[ndup++] = this;
}
return ndup;
}