What happens when if statement goes true (in this code)?

Question

There is a problem in codingbat.com which you're supposed to remove "yak" substring from the original string. and they provided a solution for that which I can't understand what happens when the if statement goes true!

public String stringYak(String str) {
  String result = "";

  for (int i=0; i<str.length(); i++) {
    // Look for i starting a "yak" -- advance i in that case
    if (i+2<str.length() && str.charAt(i)=='y' && str.charAt(i+2)=='k') {
      i =  i + 2;
    } else { // Otherwise do the normal append
      result = result + str.charAt(i);
    }
  }

  return result;
}

It just adds up i by 2 and what? When it appends to the result string?

Link of the problem: https://codingbat.com/prob/p126212

Answer 1

The provided solution checks for all single characters in the input string. For this i is the current index of the checked character. When the current char is not a y and also the (i+2) character is not a k the current char index is advanced by 1 position.

Example:

yakpak
012345
i

So here in the first iteration the char at i is y and i+2 is a k , so we have to skip 3 chars. Keep in mind i is advanced by 1 everytime. So i has to be increased by 2 more. After this iteration i is here

yakpak
012345
   i

So now the current char is no y and this char will get added to the result string.

But it's even simpler in Java as this functionality is build in with regex:

public String stringYak(String str) {
  return str.replaceAll("y.k","");
}

The . means every char.

Answer 2

If i is pointing at a y and there is as k two positions down, then it wants to skip the full y*k substring, so it add 2 to i so i now refers to the k . WHen then loop continues, i++ will skip past the k , so in effect, the entire 3-letter y*k substring has been skipped.