Recursively remove adjacent duplicate from ArrayList of integers, without removing both-CodePudding

I am writing a method to remove an adjacent duplicate value in an ArrayList of Integer.

public static void remove2InARow(ArrayList<Integer> list) {
    for (int i = 0; i < list.size() - 1; i  ) {
        if (list.get(i) == list.get(i 1)) {
            list.remove(i);
        }
    }
}

If you passed in [3,4,3,3] as a parameter, the output would be [3,4,3].

This implementation becomes problematic when the same value is repeated more than 2 times. For example, [1, 2, 5, 4, 6, 6, 6, 1, 2] becomes [1, 2, 5, 4, 6, 6, 1, 2] when it should be [1, 2, 5, 4, 6, 1, 2]. Similarly, [n, ..., n] should become [n].

Is there a way to adapt my implementation to be recursive? Does it even need to be recursive?

CodePudding user response：

It certainly does not need to be recursive!

The source of your problem is that removing elements from a collection while iterating over it can lead to some unexpected behaviour, try not to touch the list while iterating over it, then once you're done - remove the elements you need to.

CodePudding user response：

import java.util.stream.Collectors;

public static void remove2InARow(ArrayList<Integer> list) {;

list= list.stream().distinct().collect(Collectors.toList());

System.out.println(list);

}

Maybe it'll help you!

CodePudding user response：

public static void remove2InARow(ArrayList<Integer> list) {
    for (int i = 0; i < list.size() - 1; i  ) {
        if (list.get(i) == list.get(i 1)) {
            list.remove(i);
            i--;
        }
    }
}

This worked for me.