repeatFront

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Given a string and an int n, return a string made of the first n characters of the string, followed by the first n-1 characters of the string, and so on. You may assume that n is between 0 and the length of the string, inclusive (i.e. n >= 0 and n <= str.length()).
repeatFront("Chocolate", 4) → "ChocChoChC"
repeatFront("Chocolate", 3) → "ChoChC"
repeatFront("Ice Cream", 2) → "IcI"

public String repeatFront(String str, int n) 
{
     String res=str.substring(0,n);
     for(int i=1;i<n;i++)
     {
            res=res+str.substring(0,n-i);
     }
     return res;
}