Question

Java Generic 2D Linked List Problem

How to convert a 1D linked List into multiple linked lists with sequential values together?

//Example 1: [1,1,2,3,3] becomes [[1,1],[2],[3,3]]
//Example 1: [1,1,2,1,1,2,2,2,2] becomes [[1,1],[2],[1,1],[2,2,2,2]]
//Example 3: [1,2,3,4,5] becomes [[1],[2],[3],[4],[5]]

public <T> List<List<T>> convert2D(List<T> list) {

// Given a 1D, need to combine sequential values together.

}

Answer 1

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Test {
        //Example 1: [1,1,2,3,3] becomes [[1,1],[2],[3,3]]
        //Example 1: [1,1,2,1,1,2,2,2,2] becomes [[1,1],[2],[1,1],[2,2,2,2]]
        //Example 3: [1,2,3,4,5] becomes [[1],[2],[3],[4],[5]]
        public static <T> List<List<T>> convert2D(List<T> list) {
                
                List<List<T>> result = new ArrayList<>();
                
                T prevVal = null;
                for(int i=0; i<list.size(); i++) {
                        T val = list.get(i);
                        
                        if(i == 0 || val != prevVal) {
                                result.add(new ArrayList<>());
                                prevVal = val;
                        }
                        
                        result.get(result.size() - 1).add(val);
                }
                
                return result;
        }


        
        public static void main(String[] args) {
                System.out.println(convert2D(new ArrayList<>(Arrays.asList(1, 1, 2, 3, 3))));
                System.out.println(convert2D(new ArrayList<>(Arrays.asList(1,1,2,1,1,2,2,2,2))));
                System.out.println(convert2D(new ArrayList<>(Arrays.asList(1,2,3,4,5))));
                
        }
}

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