合并list1中的两个数组列表，同时保持排序。[英] merge two arraylist lists in list1 while it remain sorted

问题描述

In my assignment the third step is to Call the method merge to merge the two lists in list1 so that the list1 remains sorted.

I write my code but it doesn't work well , the output show wrong because it important to be sorted

 public static void merge (ArrayList<Integer> list1, ArrayList<Integer> list2)
 {
        int i;
        int n=list1.size();
        int pos , j=0;

        for (pos =0 ;pos<n ; pos++)
        {
            for ( i=0 ; i<n ; i++)
                if (list1.get(j)>list2.get(pos))
                    list1.add(pos,list2.get(pos));
                else 
                    j++;
       } 
 }

推荐答案

You only need one for loop assuming both lists are sorted:

public static void merge(List<Integer> l1, List<Integer> l2) {
    for (int index1 = 0, index2 = 0; index2 < l2.size(); index1++) {
        if (index1 == l1.size() || l1.get(index1) > l2.get(index2)) {
            l1.add(index1, l2.get(index2++));
        }
    }
}  

If l2 isn't sorted, you need two loops:

public static void merge(List<Integer> l1, List<Integer> l2) {
    for (int index2 = 0; index2 < l2.size(); index2++) {
        for (int index1 = 0; ; index1++) {
            if (index1 == l1.size() || l1.get(index1) > l2.get(index2)) {
                l1.add(index1, l2.get(index2));
                break;
            }
        }
    }
}

其他推荐答案

Easy fix: sort afterwards.

list1.addAll(list2);
Collections.sort(list1);

Use sets to avoid duplicates.

其他推荐答案

public static void merge (ArrayList<Integer> list1, ArrayList<Integer> list2)
{
    list1.addAll(list2);
    Collections.sort(list1);
}