Implement strstr

PROBLEM :

Your task  is to implement the function strstr. The function takes two strings as arguments(s,x) and  locates the occurrence of the string x in the string s. The function returns and integer denoting  the first occurrence of the string x .

Input:
The first line of input contains an integer T denoting the no of test cases . Then T test cases follow. The first line of each test case contains two strings str and target.

Output:
For each test case in a new line output will be an integer denoting the first occurrence of the target  string in the string s. Return -1 if no match found.

Constraints:
1<=T<=100
1<=length of (s,x)<=1000

Example:

Input
2
GeeksForGeeks Fr
GeeksForGeeks For

Output
-1
5

--------------------------------------------------------------------------------
SIMPLE c++ IMPLEMENTATION :( using KMP algo )
--------------------------------------------------------------------------------

/* The function should return position where the target string
   matches the string str
Your are required to complete this method */

void prefix_table(string ,int [],int ) ;
int strstr(string s, string x)
{
    int l1,l2 ;
    l1=s.length() ;
    l2=x.length() ;
   
    int arr[l2] ;
   
    prefix_table(x,arr,l2) ;
   
    int i,j ;
    i=0;
    j=0 ;
   
    while(i<l1)
    {
        if(s[i]==x[j])
        {
            if(j==l2-1)
                return i-j ;
            else
            {
                i++ ;
                j++ ;
            }
        }
        else if(j>0)
            j=arr[j-1] ;
        else
            i++ ;
    }
   
    return -1 ;
}

void prefix_table(string str,int arr[],int len)
{
    int i,j ;
    i=1 ;
    j=0 ;
    arr[j]=0 ;
   
    while(i<len)
    {
        if(str[i]==str[j])
        {
            arr[i]=j+1 ;
            j++ ;
            i++ ;
        }
        else if(j==0)
        {
            arr[i]=0 ;
            i++ ;
        }
        else
        {
            j=arr[j-1] ;
        }
    }
}

---------------------------------------------------------------------------------