I want to build an algorithm that takes into account a list of integers, sort it.

The idea is: iterate over the list of integers, the first value gets into a new list; the following value is compared with the only existing value in the new list and put it in before or after, and so on.

import java.util.*;
import java.util.function.Supplier;
import java.util.ArrayList;
  
public class SortLists {
    
    public static void main(String args[])
    {
  
        // list [5,1,4,2,8]
        List<Integer> list = new ArrayList<Integer>();
        list.add(5);
        list.add(1);
        list.add(4);
        list.add(2);
        list.add(8);

        System.out.println("list : "   list.toString());
        
        // new empty list
        List<Integer> list2 = new ArrayList<Integer>();
        
        // iterate over the integer list
        for (int i = 0; i < list.size(); i  ){
        //int i=2;
        
            // *** 1st iteration - add the value to the list2
            
            if (i == 0){
                list2.add(list.get(i));
            } else {
                
                // *** in the next interations, compare with the existing values in list2
                for (int j = 0; j < list2.size(); j  ){

                    
                    // *** Note: this if is unecessary but I got an error with list2.get(j)
                    if (j==0){
                        // if the value from list is lower than the only value in list2, put in index 0
                        if (list.get(i) < list2.get(0) ) {
                             list2.add(j,list.get(i));
                        } 
                        
                    }else{
                         
                        if (list.get(i) < list2.get(j) ) {
                             //list2.add(j,list.get(i)); // GIVES ERROR!
                             System.out.println("index " j " value " list.get(i));
                             
                        } else {
                            //list2.add(list.get(i)); //GIVES ERROR!
                            System.out.println("else: index " j " value " list.get(i));
                        }
                    }
                }
            }
        }
        //list2.add(1,4); // no error if add manually here
        System.out.println("list2 : "   list2.toString());
        
    }
}

The 5 and 1 are correctly inserted in list2.

The other two list2.add, if I uncomment them, the execution doesn't stop.

CodePudding user response：

the execution doesn't stop

You get into an infinite loop because in the inner for loop you are adding elements to the second list while iterating over the list.

Besides, you are overcomplicating things unnecessarily. Just store the first index for which list.get(i) < list2.get(j) is true. If such an index exists, add the i-th element from list one to list two at that index. Otherwise add the i-th element from list one to the end of list two.

public static void main(String[] args) {
    List<Integer> list = new ArrayList<Integer>();
    list.add(1);
    list.add(5);
    list.add(1);
    list.add(4);
    list.add(2);
    list.add(8);

    System.out.println("list : "   list.toString());

    List<Integer> list2 = new ArrayList<Integer>();
    
    list2.add(list.get(0));
    
    for (int i = 1; i < list.size(); i  ){
        int index = list2.size();
        for(int j = 0; j < list2.size(); j  ){
            if (list.get(i) < list2.get(j)){
                index = j;
                break;
            }
        }
        list2.add(index,list.get(i));
    }

    System.out.println(list);
    System.out.println(list2);
}

CodePudding user response：

Add j after the commented code that gives an error since you are increasing the list size by one. Otherwise it is an infinite loop.