Replace by X

PROBLEM :

Given a string and a pattern, Replace all the continuous occurrence of pattern with a single X in the string. For a clear view see the example below.

Input:

The first line of input contains an integer T denoting the number of test cases.
The first line of each test case is string str.
The second line of each test case contains a string s,which is a pattern.

Output:

Print the modified string str.

Constraints:

1 = T = 100
1 = size of str,s = 1000

Example:

Input
2
abababcdefababcdab
ab
geeksforgeeks
geeks

Output
XcdefXcdX
XforX

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SIMPLE c++ IMPLEMENTATION :
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#include<iostream>
using namespace std;
#include<string.h>
#include<malloc.h>

char* Replace_by_X(char *,char *) ;
int compare(char *,char *,int ) ;

int main()
 {
int t ;
char *str,*patt ;
str=(char*)malloc(1000*sizeof(char)) ;
patt=(char*)malloc(1000*sizeof(char)) ;
cin>>t ;
while(t--)
{
   cin>>str>>patt ;
 
   str=Replace_by_X(str,patt) ;
   cout<<str<<endl  ;
}
return 0;
}

char* Replace_by_X(char *str,char *patt)
{
    char *ans ;
    ans=(char*)malloc(1000*sizeof(char)) ;
   
    int l1,l2,k,i ;
    l1=strlen(str) ;
    l2=strlen(patt) ;
   
    k=0 ;
   for(i=0;i<l1;i++)
   {
       if((str[i]==patt[0])&&(compare(str,patt,i)))
       {
           if(ans[k-1]!='X')
                ans[k++]='X' ;
           i=i+l2-1 ;
       }
       else
        ans[k++]=str[i] ;
   }
   ans[k]='\0' ;
   return ans ;
}

int compare(char * str,char * patt,int pos)
{
    int l=strlen(patt);
    int i ;
   
    for(i=0;i<l;i++)
    {
        if(patt[i]!=str[pos+i])
            return 0 ;
    }
    return 1 ;
}

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