Java – moves characters in a string to the left

I'm a novice at stack overflow. I have a lab problem with a programming class that has been avoiding me The problem requires us to move the element of string s to the left K times For example, if the inputs are "Hello world" and 3, "Hello world" is output For very large K values, it must also work relatively efficiently This is what I have done so far:

String cyclicLeftShift(String s,int k){
   String result="";  

   for(int i=0;i<k;i++){
       result = s.substring(1,s.length() - 1) +s.charAt(0);

       s=result;
    }
    return s;
}

My main problem is that the last character of the original string is constantly overwritten by subsequent iterations of the loop I've tried a lot of permutations, including converting the whole thing into an array (which violates the efficiency limit in the original problem) I think there's a little thing I didn't get. I wonder if anyone can give me a push in the right direction?

thank you!

Solution

What you want is to split the string at position K and merge the two parts together again, but in the opposite order

public static String cyclicLeftShift(String s,int k){
    k = k%s.length();
    return s.substring(k) + s.substring(0,k);
}

Test method:

public static void main(String[] args)
{
    String test = "Hello World";
    for(int i = 0; i < test.length()*3; i++)
        System.out.println(cyclicLeftShift(test,i));
}

Output:

Hello World
ello WorldH
llo WorldHe
lo WorldHel
o WorldHell
 WorldHello
WorldHello 
orldHello W
rldHello Wo
ldHello Wor
dHello Worl
Hello World
ello WorldH
llo WorldHe
lo WorldHel
o WorldHell
 WorldHello
WorldHello 
orldHello W
rldHello Wo
ldHello Wor
dHello Worl
Hello World
ello WorldH
llo WorldHe
lo WorldHel
o WorldHell
 WorldHello
WorldHello 
orldHello W
rldHello Wo
ldHello Wor
dHello Worl