please help me to find Bug in my Code (segmentation fault) - c

Question

i am tring to solve this http://www.spoj.com/problems/LEXISORT/ question
it working fine in visual studio compiler and IDEone also but when i running in SPOJ compiler it is getting SEGSIGV error
Here my code goes
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
char *getString();
void lexisort(char **str,int num);
void countsort(char **str,int i,int num);
int main()
{
int num_test;
int num_strings;
char **str;
int i,j;
scanf("%d",&num_test);
for(i=0;i<num_test;i++)
{
scanf("%d",&num_strings);
str=(char **)malloc(sizeof(char *)*num_strings);
for(j=0;j<num_strings;j++)
{
str[j]=(char *)malloc(sizeof(char)*11);
scanf("%s",str[j]);
}
lexisort(str,num_strings);
for(j=0;j<num_strings;j++)
{
printf("%s\n",str[j]);
free(str[j]);
}
free(str);
}
return 0;
}
void lexisort(char **str,int num)
{
int i;
for(i=9;i>=0;i--)
{
countsort(str,i,num);
}
}
void countsort(char **str,int i,int num)
{
int buff[52]={0,0},k,x;
char **temp=(char **)malloc(sizeof(char *)*num);
for(k=0;k<52;k++)
{
buff[k]=0;
}
for(k=0;k<num;k++)
{
if(str[k][i]>='A' && str[k][i]<='Z')
{
buff[(str[k][i]-'A')]++;
}
else
{
buff[26+(str[k][i]-'a')]++;
}
}
for(k=1;k<52;k++)
{
buff[k]=buff[k]+buff[k-1];
}
for(k=num-1;k>=0;k--)
{
if(str[k][i]>='A' && str[k][i]<='Z')
{
x=buff[(str[k][i]-'A')];
temp[x-1]=str[k];
buff[(str[k][i]-'A')]--;
}
else
{
x=buff[26+(str[k][i]-'a')];
temp[x-1]=str[k];
buff[26+(str[k][i]-'a')]--;
}
}
for(k=0;k<num;k++)
{
str[k]=temp[k];
}
free(temp);
}

Answer 1

Generally speaking, these online judge programs give an example input (in this case, that input appears to work perfectly), but also use a set of harder hidden inputs.
In this case, what happens if the input string has a space in it? For example, an input of:
1
2
hello orld
whateverss
In this case, your scanf("%s",str[j]); will not properly read that input line. I'd suggest switching over to a getline style interface, rather than a scanf style interface.