My code shows segmentation fault on hackerrank.What will happen if I use long long int?
Here is the link https://www.hackerrank.com/challenges/crush/problem?isFullScreen=true
My code is:
#include <stdio.h>
int main()
{
int n, m;
scanf("%d%d", &n, &m);
int queries[m][3];
for (int i = 1; i <= m; i++) {
scanf("%d", &queries[i][1]);
scanf("%d", &queries[i][2]);
scanf("%d", &queries[i][3]);
}
int a[n];
for (int i = 1; i <= n; i++)
a[i] = 0;
for (int i = 1; i <= m; i++) {
for (int j = queries[i][1]; j <= queries[i][2]; j++)
a[j] = a[j] + queries[i][3];
}
int max;
max = 0;
for (int i = 1; i <= n; i++) {
if (max < a[i])
max = a[i];
}
printf("%d", max);
return 0;
}
Array index out of bounds at .
a[j]=a[j]+queries[i][3];
because Array index 3 is past the end of the array (which contains 3 elements) thus 2 is the last index.
and when using the for loops to access the array you might need to start from 0
Code
#include<stdio.h>
int main()
{
int n,m;
scanf("%d%d",&n,&m);
int queries[m][3];
for( int i=0;i<m;i++)
{
scanf("%d",&queries[i][0]);
scanf("%d",&queries[i][1]);
scanf("%d",&queries[i][2]);
}
int a[n];
for(int i=0;i<n;i++)
a[i]=0;
for(int i=0;i<m;i++)
{
for(int j=queries[i][0];j<=queries[i][1];j++)
a[j]=a[j]+queries[i][2];
}
int max;
max=0;
for(int i=0;i<n;i++)
{
if(max<a[i])
max=a[i];
}
printf("%d",max);
return 0;
}
You have array index out of bounds error at this line:
a[j] = a[j] + queries[i][3];
What value can i take?
To avoid similar errors in the future you may want to consider usage of tools for static code analysis. For example, cppcheck is a free and open source tool that can detect this error:
stackoverflow/c-issue.c:23:34: error: Array 'queries[2147483648][3]' accessed
at index queries[*][3], which is out of bounds.
[arrayIndexOutOfBounds]
a[j] = a[j] + queries[i][3];
In every loop you are passing boundaries of your array which will cause undefined behavior.
when you declare int arr [num] , if you access arr[x] while x=>num , you are passing boundaries of your array and that will cause undefined behavior , which means you can't predict what will happen.
look
int main()
{
int n, m;
scanf("%d%d", &n, &m);
int queries[m][3];
for (int i = 0; i < m; i++) {
scanf("%d", &queries[i][0]);
scanf("%d", &queries[i][1]);
scanf("%d", &queries[i][2]);
}
int a[n];
for (int i = 0; i < n; i++)
a[i] = 0;
for (int i = 0; i < m; i++) {
for (int j = queries[i][0]; j <= queries[i][1]; j++)
a[j] = a[j] + queries[i][2];
}
int max;
max = 0;
for (int i = 0; i < n; i++) {
if (max < a[i])
max = a[i];
}
printf("%d", max);
return 0;
}
Related
Im trying to sort a matrix by the sum of its row's digits, from highest to lowest. I dont know if i explained that correctly so here's some photos explaining it.
This is what my code outputs. Basically, it asks you for m and n, which are the dimensions of the matrix. In this example it's a 3x4, 3 rows and 4 columns. Then, the matrix should be sorted by rows, by the sum of row's digits. Which means, instead of what's being outputted in the picture above, the correct result should be this:
I have no idea how to sort this from highest to lowest, i have been trying for hours to no avail.
Here's my code:
#include <stdio.h>
#define N 30
void main(){
double a[N][N], s[N], p;
int i, j, m, n, max;
while(1){
printf("\nm, n? ");
scanf("%d%d", &m, &n);
if(m <= 0 || m > N || n <=0 || n > N)
break;
for(i = 0; i < m; i++){
printf("%2d. row? ", i+1);
for(j = 0; j < n; scanf("%lf", &a[i][j++]));
}
for(i = 0; i < m; i++)
for(s[i] = j = 0; j < n; s[i] += a[i][j++]);
for(j = 0; j < n - 1; j++){
for(max = i, j = i+1; j < n; j++)
if(s[j] > s[max])
max = i;
if(max != j){
p = s[j];
s[j] = s[max];
s[max] = p;
for(j = 0; j < m; j++){
p = a[j][i];
a[j][i] = a[j][max];
a[j][max] = p;
}
}
}
printf("New matrix: \n");
for(i = 0; i < m; i++){
for(j = 0; j < n; printf("%8.2lf", a[i][j++]));
printf("\n");
}
for(j = 0; j < m; j++)
printf("-------------");
printf("\n");
for(j = 0; j < m; printf("%8.2f \n", s[j++]));
printf("\n");
}
}
You can sort the rows of the matrix from highest to lowest, using a simple bubble sort algorithm.Your code modified below:
int main() {
double a[N][N], s[N], p;
int i, j, m, n, max;
while (1) {
printf("\nm, n? ");
scanf("%d%d", & m, & n);
if (m <= 0 || m > N || n <= 0 || n > N)
break;
for (i = 0; i < m; i++) {
printf("%2d. row? ", i + 1);
for (j = 0; j < n; scanf("%lf", & a[i][j++]));
}
for (i = 0; i < m; i++)
for (s[i] = j = 0; j < n; s[i] += a[i][j++]);
for (i = 0; i < m - 1; i++) { // modified here
for (j = i + 1; j < m; j++) { // modified here
if (s[j] > s[i]) { // modified here
p = s[i];
s[i] = s[j];
s[j] = p;
for (int k = 0; k < n; k++) {
p = a[i][k];
a[i][k] = a[j][k];
a[j][k] = p;
}
}
}
}
printf("New matrix: \n");
for (i = 0; i < m; i++) {
for (j = 0; j < n; printf("%8.2lf", a[i][j++]));
printf("\n");
}
for (j = 0; j < m; j++)
printf("-------------");
printf("\n");
for (j = 0; j < m; printf("%8.2f \n", s[j++]));
printf("\n");
}
return 0;
}
Here's how i modified your code to achieve that:
Initialize a loop variable i to 0.
In the outer loop, run the inner loop j from i+1 to m-1.
In the inner loop, compare the sum of the row i with the sum of row
j. If the sum of row j is greater than the sum of row i, swap the
rows using a temporary variable.
After the inner loop finishes, increment the value of i by 1. Repeat
the outer loop until i becomes equal to m-1.
Output:
You can just use qsort to let it handle the sorting and item swapping. Then you only need to write the code for comparing two rows with each other.
Given something like this:
int matrix[3][4] =
{
{1,2,3,4},
{5,6,7,8},
{9,1,2,3},
};
You'd call qsort as:
qsort(matrix, 3, sizeof(int[4]), compare);
The only complexity is implementing the comparison callback function. There's two things to consider there:
We've told qsort that we have an array of 3 items, each of type int[4]. So the void pointers it passes along to us will actually be pointers to type int[4]. That is: int(*)[4].
qsort sorts in ascending order by default, where the item considered "less" ends up first. So we need to tweak that to get the largest item first.
Example:
int compare (const void* obj1, const void* obj2)
{
const int (*ptr1)[4] = obj1;
const int (*ptr2)[4] = obj2;
size_t sum1=0;
size_t sum2=0;
for(size_t i=0; i<4; i++)
{
sum1 += (*ptr1)[i];
sum2 += (*ptr2)[i];
}
if(sum1 > sum2) // largest sum considered "less" for qsort
return -1;
else
return 1;
return 0;
}
sum1 < sum2 would have placed the smallest row first.
Full example:
#include <stdio.h>
#include <stdlib.h>
int compare (const void* obj1, const void* obj2)
{
const int (*ptr1)[4] = obj1;
const int (*ptr2)[4] = obj2;
size_t sum1=0;
size_t sum2=0;
for(size_t i=0; i<4; i++)
{
sum1 += (*ptr1)[i];
sum2 += (*ptr2)[i];
}
if(sum1 > sum2) // largest sum considered "less" for qsort
return -1;
else
return 1;
return 0;
}
void print_matrix(size_t col, size_t row, int matrix[col][row])
{
for(size_t i=0; i<col; i++)
{
for(size_t j=0; j<row; j++)
{
printf("%d,", matrix[i][j]);
}
puts("");
}
}
int main (void)
{
int matrix[3][4] =
{
{1,2,3,4},
{5,6,7,8},
{9,1,2,3},
};
print_matrix(3,4,matrix);
puts("");
qsort(matrix, 3, sizeof(int[4]), compare);
print_matrix(3,4,matrix);
}
I've been trying to sort columns in a matrix (the dimensions are m,n <= 10) via the lexicographical order (if the columns share the same element, then we compare the elements in the row beneath etc.) with some additional conditions. I need to use functions to print the matrix, input random integers up to 5 as its elements and finally arrange the matrix. I think I got the printing and random inputs correctly but I can't figure out the sorting. Plus I can't use global variables which I have no idea how to do, since I haven't been shown. An example matrix would be :
#include <stdio.h>
#include <stdlib.h>
int main()
{
int m, n;
int mat[10][10];
void print_matrix()
{
int i, j;
for (i = 0; i < m; i++)
{
for (j = 0; j < n; j++)
{
printf("%d ", mat[i][j]);
}
printf("\n");
}
}
void random_int()
{
int i, j;
srand((unsigned)time(NULL));
for (i = 0; i < m; i++)
{
for (j = 0; j < n; j++)
{
mat[i][j] = rand() % 5;
}
}
}
void arrange()
{
int i, j, k, a;
for (j = 0; j < n; ++j)
{
for (i = 0; i < m; ++i)
{
for (k = i + 1; k < m; ++k)
{
if (mat[i][j] < mat[k][j])
{
a = mat[i][j];
mat[i][j] = mat[k][j];
mat[k][j] = a;
}
}
}
}
}
printf("Input the number of rows : ");
scanf("%d", &m);
printf("Input the number of columns: ");
scanf("%d", &n);
random_int(mat[m][n]);
print_matrix(mat[m][n]);
arrange(mat[m][n]);
print_matrix(mat[m][n]);
return 0;
}
Try this solution(will work for input 0-8 only), also used global variables:
There have multiple solutions. but is the easiest one.
I have converted each of the columns as an integer value. then bubble sorted the integers. After sorting. I have then converted the integer value to digits. (You have to know how to convert individual digits to multiple digit integer and multiple digit integers to single-digit.
Note I have added one(1) with each digit. Because the input can be zero(0). if you convert 0 0 2 1 to an integer will be only 21. the first two digits lost. So I have added 1. so 0 0 2 1 will be converted to 1132. I have done (added 1) for each input(deducted 1 after sorting). so it will not affect other inputs. Be careful input have to be from(0 to 8)
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int m, n;
int mat[10][10];
int generatedNumber[10];
void print_matrix()
{
printf("The matrix is:\n");
int i, j;
for (i = 0; i < m; i++)
{
for (j = 0; j < n; j++)
{
printf("%d ", mat[i][j]);
}
printf("\n");
}
}
void random_int()
{
int i, j;
srand((unsigned)time(NULL));
for (i = 0; i < m; i++)
{
for (j = 0; j < n; j++)
{
mat[i][j] = rand() % 5;
}
}
}
void arrange()
{
int i, j, k, a;
for (j = 0; j < n; ++j)
{
int number = 0;
for (i = 0; i < m; ++i)
{
number = number * 10 + mat[i][j] + 1;///Adding one for avoiding zero(0)
}
generatedNumber[j] = number;
}
for(i = 0; i < n; i++)
{
for(j = 0; j < n-i-1; j++)
{
if( generatedNumber[j] > generatedNumber[j+1])
{
// swap the elements
int temp = generatedNumber[j];
generatedNumber[j] = generatedNumber[j+1];
generatedNumber[j+1] = temp;
}
}
}
for(i = 0; i < n; i++)///columwise
{
int generatedColumnvalue = generatedNumber[i];
for(j = m -1; j>= 0; j--)///row wise and fro last vaue to first
{
mat[j][i] = (generatedColumnvalue%10)-1;///removing extra added 1
generatedColumnvalue/=10;
}
}
}
int main()
{
printf("Input the number of rows : ");
scanf("%d", &m);
printf("Input the number of columns: ");
scanf("%d", &n);
random_int();
print_matrix();
arrange();
print_matrix();
return 0;
}
I wrote to program in C to attempt to print array elements in descending order. I wrote a nested loop which would find the maximum element of the array and the value of the element would be set to later 0. This process would be repeated for all the elements. However, in the output, I am getting the first 2-3 values as desired but the remaining values are garbage. Any suggestions?
int main() {
int i, j, n, k;
scanf("%d\n", &n);
int a[100], b[100];
for (i = 0; i < n; i++) {
scanf("%d", &a[i]);
}
for (i = 0; i < n; i++) {
int max = a[i];
for (j = i; j < n; j++) {
if (a[j] > max) {
max = a[j];
b[i] = max;
}
}
for (k = 0; k < n; k++) {
printf("%d", a[k]);
if (a[k] == b[i]) {
a[k] = 0;
}
}
printf("\n");
}
for (i = 0; i < n; i++) {
printf("%d ", b[i]);
}
}
The main issue is that you only set b[i] = max; when you find a new max, but since you initialized max to be a[i] it could happen that it already holds the maximum value. So the if never executes, therefore b[i] is not written and there's garbage value in it. You should move this line from the if after that for loop.
Another issue is that you initialize j with i in this loop. You should initialize it to 0.
The changed part:
for (j = 0; j < n; j++) {
if (a[j] > max) {
max = a[j];
}
}
b[i] = max;
I need to make a little project but I completely don't know how. Im giving matrix A of size n, and it have to return me matrix B which is matrix A with zeroed first and penultimate column. All I did is
#include<stdio.h>
#include<math.h>
int main()
{
int i,n,j,;
int tab[n][n];
printf("Size of matrix:");
scanf("%d",&n);
for (i = 0; i < n; i++)
for (j = 0; j < n; j++)
{
printf("A[%d][%d]=",i,j);
scanf("%lf",&tab[i][j]);
}
printf("Data:");
printf("Matrix A[%d][%d]",n,m);
}
Which I think should let me to type my matrix. What I should do next? Please help me.
There are a lot of errors in your code, the variable m is not declared, the double array is declared with n non-initialized. As the size of matrix is only known at runtime (entered by user), you need to use dynamic memory allocation functions to allocate memory for your matrix.
Try this code:
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
int i, j, n;
printf("Size of matrix: ");
scanf("%d", &n);
int *tab = (int*)malloc(sizeof(int)*n*n);
for (i = 0; i < n; i++)
{
for (j = 0; j < n; j++)
{
printf("A[%d][%d]=",i,j);
scanf("%d",(tab+i*n+j));
}
}
for (i = 0; i < n; i++)
{
*(tab+i*n) = 0;
*(tab+i*n+n-2) = 0;
}
//Print tab
for (i = 0; i < n; i++)
{
for (j = 0; j < n; j++)
{
printf("%d ", *(tab+i*n+j));
}
printf("\n");
}
return 0;
}
I'm working on a project (written in C) involving matrix factorization and I need some help.
My objective is to allocate memory for an upper triangular matrix and I want to access it via algebraic row and column notation (i.e. i,j in {1,2,...,n} instead of i,j in {0,1,...,n-1}).
For example, in a 5x5 matrix I should be able to access the [3][4] element if I input matrix[3][4].
My code for a non-algebraic index upper triangular matrix looks like this:
double** malloc_sup_matrix (int n)
{
double** L;
int i;
L = (double**)malloc((n)*sizeof(double*));
if(L == NULL)
printerror("allocating space for the matrix (rows).");
for(i = 0; i < n; i++)
{
L[i] = (double*)malloc((n-i)*sizeof(double));
if(L[i] == NULL)
printerror("allocating space for the matrix (cols).");
L[i]-=i;
}
return L;
}
My code for the algebraic index one (I'm not checking if the allocated space is null yet, I'll do it when I stop messing around with this):
int** m;
int i, n;
n = 10;
m = (int**)malloc((n+1)*sizeof(int*));
for(i = 0; i < n; i++)
{
m[i] = (int*)calloc((n+1)-(i),sizeof(int));
m[i] -= i;
}
m--;
for(i = 0; i < n; i++)
{
m[i]--;
}
It works just the way I want it, but I have issues when freeing the space I've used. This is the way I'm doing it:
for(i = 1; i <= n; i++)
{
m[i]++;
}
for(i = 0; i < n; i++)
{
m[i] += (i);
free(m[i]);
}
m++;
free(m);
Do you guys have any suggestions? Thank you so much in advance ^^.
There's a problem on this line:
m--;
for(i = 0; i < n; i++)
{
m[i]--;
}
You're decrementing m, but then go ahead and index it from 0 ... I guess you may end up messing up the heap structures.
I managed to have your code valgrind error-free like this:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
int** m;
int i, j, n;
n = 10;
m = (int**)malloc((n+1)*sizeof(int*));
for(i = 0; i < n; i++)
{
m[i] = (int*)calloc((n+1)-(i), sizeof(int));
m[i] -= i;
}
for(i = 0; i < n; i++)
{
m[i]--;
}
m--;
/* Access it like m[1][1] ... m[n][n], m[i][j] (with i <= j) */
/*
for (i = 1; i <= n; i++) {
for (j = i; j <= n; j++) {
m[i][j] = i+j;
}
}
*/
m++;
for(i = 0; i < n; i++)
{
m[i]++;
}
for(i = 0; i < n; i++)
{
m[i] += (i);
free(m[i]);
}
free(m);
return 0;
}