Given a string and a non-empty substring sub, Count sub in given string

Given a string and a non-empty substring sub, compute recursively the number of times that sub appears in the string, without the sub strings overlapping.

strCount("catcowcat", "cat") → 2
strCount("catcowcat", "cow") → 1
strCount("catcowcat", "dog") → 0




If i want to know that a substring exists in a given string or not, always try to use indexOf keyword rather than '==' operator. Because

String is immutable. i.e. Strings cannot be altered. When you alter a string (by adding to it for example), you are actually creating a new string object.




WorstCase:

static int strCount(String str, String sub) {

 int n = sub.length();
 int len = str.length();

 if(len < n) return 0;

 String tmp = str.substring(0,n);

 if(tmp.contains(sub))   // never use this in string (tmp == sub)
 {
 return strCount(str.substring(n, len), sub)+1;
  }
 else {
       return strCount(str.substring(1,len), sub);
 }

}


Better solution:

Use of  'indexOf ' string inbuild method:

static int strCount(String str, String sub)
{                                                
  return strCountUtil(str,sub,sub.length());
}


private static int strCountUtil(String str, String sub, int n)
{
int len = str.length();
if(len < n) return 0;
int index = str.indexOf(sub);
if(index >= 0)
{
return 1 + strCountUtil(str.substring(index+n), sub, n);
}

return 0;
}



private static int

"catdogccatca"
          |
 dogccatca
         |
     ca