The challenge

You are given an array of strings and your task is to remove all consecutive duplicate letters from each string in the array.

For example:

  • dup(["abracadabra","allottee","assessee"]) = ["abracadabra","alote","asese"].
  • dup(["kelless","keenness"]) = ["keles","kenes"].

Strings will be lowercase only, no spaces. See test cases for more examples.

The solution in Java code

Option 1 (using StringBuilders):

class Solution{    
    public static String[] dup(String[] arr){
        String[] strings = new String[arr.length];

        for (int h = 0; h < arr.length; h++) {

            String str = arr[h];

            StringBuilder sb = new StringBuilder();
            char current = 0;
            char last = 0;
            for (int i = 0; i < str.length(); i++) {
                current = str.charAt(i);
                if (current!=last) sb.append(current);
                last = current;
            }
            strings[h] = sb.toString();

        }

        return strings;
    }
}

Option 2 (reusing the input array):

class Solution{    
    public static String[] dup(String[] arr){
        for(int i = 0; i < arr.length; i++)
            arr[i] = arr[i].replaceAll("(.)\\1+", "$1");
        return arr;
    }
}

Option 3 (using Stream.of):

import static java.util.stream.Stream.of;

interface Solution {
  static String[] dup(String[] arr) {
    return of(arr).map(s -> s.replaceAll("(\\w)\\1+", "$1")).toArray(String[]::new);
  }
}

Test cases to validate our solution

import org.junit.Test;
import static org.junit.Assert.assertArrayEquals;
import org.junit.runners.JUnit4;
import java.util.*;

public class SolutionTest{
    private static Random random = new Random();    
    
    private static String unDup1(String s){
        String res = "" + s.charAt(0);
        for (int i = 1; i < s.length(); i++)        
            if (s.charAt(i-1) != s.charAt(i)) res += s.charAt(i); 
        return res;
    }

    private static String[] bvy9(String[] arr){
        String [] res = new String[arr.length]; 
        for (int i = 0; i < res.length; ++i)
          res[i] = unDup1(arr[i]);
        return res;        
    }
    
    private static int random(int l, int u){
        return random.nextInt(u-l)+l;
    }
    
    @Test
    public void basicTests(){     
        assertArrayEquals(new String[]{"andrew","picaniny","hubububo"},Solution.dup(new String[]{"aaannnndddrreew","piccaninny","hubbubbubboo"}));
        assertArrayEquals(new String[]{"abracadabra","alote","asese"},Solution.dup(new String[]{"abracadabra","allottee","assessee"}));
        assertArrayEquals(new String[]{"keles","kenes"},Solution.dup(new String[]{"kelless","keenness"}));
       
    }
    
    @Test
    public void randomTests(){ 
        String abc = "abcdefghijklmnopqrstuvwxyzabcd";
        for(int k=0;k<100;k++){
            int arrLen = random(10,20);
            int len = random(10,20);
            int i = 0;
            String [] res = new String[arrLen];
            while (i < arrLen){
              String st = "";
              int j = 0;
              while (j < len){
                int ch  = random(0,26);
                st += abc.charAt(ch);
                if (ch % 2 == 0) st+=abc.charAt(ch);
                j++;
              }  
              res[i] = st;
              i++;
            }                  
            assertArrayEquals(bvy9(res),Solution.dup(res));
        }
    }
}