Logic error? unable to duplicate?

Question about the task

R or L

Java Syntax, Level 7, Lesson 9

Resolved

the

list.add(list.get(i));

Section i feel like it adds it to the end of the list however when it returns it on completion it outputs as if it hasn't been added. what am i missing.

1. Create a list of words and populate it yourself.
2. The fix method should:
2.1. remove all words containing the letter "r" from the list
2.2. duplicate all words containing the letter "l".
2.3. if a word contains both "r" and "l", then leave it unchanged.
2.4. don't do anything to other words.

For example:
rose lyre love

Output:
lyre love love

Requirements:

The program must not read data from the keyboard.
The fix method should remove all words containing the letter "r" from the list. There is an exception: words containing both "r" and "l" should be left alone.
The fix method must duplicate words containing the letter "l" (add another instance of this word to the list). There is an exception: words containing both "l" and "r" should not be duplicated.
The fix method should not do anything with words that contain both "l" and "r".
The fix method should not do anything with words that don't contain either "l" or "r".

package com.codegym.task.task07.task0716; import java.util.ArrayList; import java.util.Collections; /* R or L */ public class Solution { public static void main(String[] args) throws Exception { ArrayList<String> list = new ArrayList<String>(); //"rose", "measure", "love", "lyre", "wade", "bark". list.add("rose"); // 0 list.add("love"); // 1 list.add("lyre"); list = fix(list); for (String s : list) { System.out.println(s); } } public static ArrayList<String> fix(ArrayList<String> list) { // write your code here for(int i = 0; i < list.size(); i++) { if(list.get(i).contains("l") && list.get(i).contains("r")) { } else if(list.get(i).contains("l") && !list.get(i).contains("r")){ list.add(i,list.get(i)); } else if(list.get(i).contains("r") && !list.get(i).contains("l")) { list.remove(i); } break; } return list; } }

Comments (2)

Popular
New
Old

You must be signed in to leave a comment

Guadalupe Gagnon

Level 37 , Tampa, United States

18 October 2019, 14:24

solution

for(int i = 0; i < list.size(); i++) {
   if(list.get(i).contains("l") && list.get(i).contains("r")){
   } else if(list.get(i).contains("l") && !list.get(i).contains("r")){
      list.add(i,list.get(i));
   } else if(list.get(i).contains("r") && !list.get(i).contains("l")) {
      list.remove(i);
   }

   break; //this line will be reached every loop cycle
}

There are problems with this code: #1 the break will be reached every loop cycle, and since that means the first loop cycle then the loop will never reach the second loop cycle #2 When you add and subtract elements it changes the size of list, here are two example of why that needs to be known: adding: list = [like, tom, cat] loop cycle will add lyre to end [like, tom, cat, lyre]; both tom and cat will be skipped because neither contain r or l, then it will test the next like, add it again, list will be [like,tom,cat,like,like] then it will move to the next like, add it again.. and again... and again infinitely until you get a OutOfMemoryError. subtracting: loop cycle 1: list equals [rose, ring, tom] i = 0, rose is pulled and contains only r so is removed, new list = [ring,tom] loop cycle 2: list equals [ring, tom] i = 1, tom is pulled and because it doesn't contain r or l is skipped list = [ring,tom] loop breaks and list is returned with ring still contained because it was skipped. Both of these issues, the break statement and the add/delete issue need to be fixed.

James Mackenzie

Level 7 , Victoria, Australia

21 October 2019, 03:25

okay so this one hurt my brain, but i got it finally, i took a weekend off to stop thinking about this one haha. finally got it after some mind numbing pain. thanks for the assist