Hi People, Below is the Problem Statement:

PS: Given a string and a non-empty substring sub, compute recursively the largest substring which starts and ends with sub and return its length.

Examples:
strDist("catcowcat", "cat") ? 9
strDist("catcowcat", "cow") ? 3
strDist("cccatcowcatxx", "cat") ? 9

Below is my Code: (Without recursion)//since i found it hard to implement with recursion.

    public int strDist(String str, String sub){    
        int idx = 0;     
        int max;    
        if (str.isEmpty()) max = 0;    
        else max=1;                        
        while ((idx = str.indexOf(sub, idx)) != -1){     
            int previous=str.indexOf(sub, idx);     
            max = Math.max(max,previous);     
            idx++;                           
        }     
     return max;    
   }

Its working for few as shown below but returns FAIL for others.

Expected This Run
strDist("catcowcat", "cat") ? 9 6 FAIL
strDist("catcowcat", "cow") ? 3 3 OK
strDist("cccatcowcatxx", "cat") ? 9 8 FAIL
strDist("abccatcowcatcatxyz", "cat") ? 12 12 OK
strDist("xyx", "x") ? 3 2 FAIL
strDist("xyx", "y") ? 1 1 OK
strDist("xyx", "z") ? 0 1 FAIL
strDist("z", "z") ? 1 1 OK
strDist("x", "z") ? 0 1 FAIL
strDist("", "z") ? 0 0 OK
strDist("hiHellohihihi", "hi") ? 13 11 FAIL
strDist("hiHellohihihi", "hih") ? 5 9 FAIL
strDist("hiHellohihihi", "o") ? 1 6 FAIL
strDist("hiHellohihihi", "ll") ? 2 4 FAIL

Could you let me whats wrong with the code and how to return the largest substring that begins and ends with sub with its respective length.