HackerRank solutions in C with medium difficulty

#include <stdio.h>
int main() 
{
    int n;
    scanf("%d", &n);
    int len = n*2 - 1;
    for(int i=0;i<len;i++){
        for(int j=0;j<len;j++){
            int min = i < j ? i : j;
            min = min < len-i ? min : len-i-1;
            min = min < len-j-1 ? min : len-j-1;
            printf("%d ", n-min);
        }
        printf("n");
    }
    return 0;
}

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */
    int n, sum=0;
    scanf("%d",&n);
    int *a = malloc(n*sizeof(int));
    for(int i=0;i<n;i++)
    {
        scanf("%d",&a[i]);
        sum+=a[i];
    }
    printf("%i",sum);
    free(a);    
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
int main()
{
    int num, *arr, i;
    scanf("%d", &num);
    arr = (int*) malloc(num * sizeof(int));
    for(i = 0; i < num; i++) {
        scanf("%d", (arr + i));
    }
    /* Write the logic to reverse the array. */
    int temp;
    for (int i; i<num/2; i++) {
        temp = *(arr+num-i-1);
        *(arr+num-i-1) = *(arr+i);
        *(arr+i) = temp;       
    }
    
    for(i = 0; i < num; i++)
        printf("%d ", *(arr + i));
    return 0;
}

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */ 
        int* nums = (int*) malloc(10 * sizeof(int));
    char c;
    
    for(int i = 0; i < 10; i++)
        *(nums+i) = 0;
    while(scanf("%c", &c) == 1)
        if(c >= '0' && c <= '9')
            (*(nums+(c-'0')))++;
    
    for(int i = 0; i < 10; i++)
        printf("%d ", *(nums+i));
    
    return EXIT_SUCCESS;   
}

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
int main() {
    char *s;
    s = malloc(1024 * sizeof(char));
    scanf("%[^n]", s);
    s = realloc(s, strlen(s) + 1);
    //Write your logic to print the tokens of the sentence here.
    for (char *c=s; *c != NULL; c++) {
    if (*c ==' ') {
    *c='n';
    }
    }
    printf("%s",s);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
struct triangle
{
	int a;
	int b;
	int c;
};
typedef struct triangle triangle;
double area(triangle t) {
  double p = (t.a + t.b + t.c) / 2.0;
  return (p * (p - t.a) * (p - t.b) * (p - t.c));
// You can also write
// return sqrt(p * (p - t.a) * (p - t.b) * (p - t.c));
// There will be no issues at all, cause even without sqrt function you'll get different values
}
void swap(triangle *t1, triangle *t2) {
  triangle temp = *t1;
  *t1 = *t2;
  *t2 = temp;
}
void sort_by_area(triangle* tr, int n) {
    int i, j;
    for (i = 0; i < n - 1; i++) {
    for (j = 0; j < n - 1 - i; j++) {
      if (area(tr[j]) > area(tr[j + 1])) {
        swap(&tr[j], &tr[j + 1]);
      }
    }
  }
}
int main()
{
	int n;
	scanf("%d", &n);
	triangle *tr = malloc(n * sizeof(triangle));
	for (int i = 0; i < n; i++) {
		scanf("%d%d%d", &tr[i].a, &tr[i].b, &tr[i].c);
	}
	sort_by_area(tr, n);
	for (int i = 0; i < n; i++) {
		printf("%d %d %dn", tr[i].a, tr[i].b, tr[i].c);
	}
	return 0;
}