Question

JAVA: when input is type ArrayList<ArrayList<Integer>> how to use java to get this solution

[ [a,b,c] , [d,e], [f] ] ----> [ [a,d,f], [a,e,f], [b,d,f], [b,e,f], [c,d,f], [c,e,f]]

[ [a,b], [a,b,c]] ----->[[a,a],[a,b],[a,c], [b,a],[b,b],[b,c]

assuming abc are integer

Thanks in advance!

Answer 1

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

public class IntCombinations {

        private static ArrayList<ArrayList<Integer>> mergeTwoLists(ArrayList<Integer> partList,
                        ArrayList<ArrayList<Integer>> overallList) {
                ArrayList<ArrayList<Integer>> result = new ArrayList<>();

                for (Integer x : partList) {
                        for (ArrayList<Integer> y : overallList) {
                                ArrayList<Integer> l2Copy = new ArrayList<>(y);
                                l2Copy.add(0, x);
                                result.add(l2Copy);
                        }
                }

                return result;
        }

        public static ArrayList<ArrayList<Integer>> generateCombs(ArrayList<ArrayList<Integer>> lists) {
                ArrayList<ArrayList<Integer>> result = new ArrayList<>();
                result.add(new ArrayList<>());
                
                for(ArrayList<Integer> x: lists) {
                        result = mergeTwoLists(x, result);
                }
                
                return result;
        }

        public static void main(String[] args) {
                ArrayList<Integer> x1 = new ArrayList<>(Arrays.asList(1, 2, 3));
                ArrayList<Integer> x2 = new ArrayList<>(Arrays.asList(4, 5));
                ArrayList<Integer> x3 = new ArrayList<>(Arrays.asList(6));
                
                ArrayList<ArrayList<Integer>> result = generateCombs(new ArrayList<ArrayList<Integer>>(Arrays.asList(x1, x2, x3)));

                for(ArrayList<Integer> x: result) {
                        System.out.println(x);
                }
                
        }

}

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