java - 如何修复我的合并排序？

Question

当我编译合并排序时，它会编译罚款，但没有输出。

这需要递归地完成。另外，我确实在主函数中运行了 printList() 函数，所以并不是我忘记打印列表。过去 30 分钟我一直盯着这个。

public void printList(){
    for(int i = 0; i <  fullNames.size(); i++){
        System.out.println(fullNames.get(i));
    }
}

public void sort(){
    fullNames = mergeSort(fullNames);
}

public ArrayList<String> extract(ArrayList<String> ex, int low, int high){
    ArrayList<String> answer = new ArrayList<String>();
    for(int i = low; i <= high; i++){
        answer.add(ex.get(i));
    }

    return answer;
}

public ArrayList<String> merge(ArrayList<String> first, ArrayList<String> second){
    int f = 0; 
    int s = 0;
    ArrayList<String> answer = new ArrayList<String>();
    while(first.size() > 0 || second.size() > 0){
        if(s != second.size() && f != first.size()){
            if(first.get(f).compareTo(second.get(s)) > 0){
                answer.add(second.get(s));
                s++;
            }

            else if(first.get(f).compareTo(second.get(s)) < 0){
                answer.add(first.get(f));
                f++;
            }
        }

        else if(f == first.size()){
            while(s != second.size()){
                answer.add(second.get(s));
                s++;
            }
        }

        else{
            while(f != first.size()){
                answer.add(first.get(f));
                f++;
            }
        }
    }

    return answer;
}
public ArrayList<String> mergeSort(ArrayList<String> names){
    int k = names.size()-1;

    if(k > 1){
        ArrayList<String> first = extract(names, 0, k / 2);
        ArrayList<String> second = extract(names, (k / 2) + 1, k);

        mergeSort(first);
        mergeSort(second);

        return merge(first, second);
    }

    else{
        return names;
    }
}

Answer 1

合并中的 while 条件永远不会为 false，因为第一个和第二个的大小永远不会在循环内调整:

while(first.size() > 0 || second.size() > 0){
        if(s != second.size() && f != first.size()){
            if(first.get(f).compareTo(second.get(s)) > 0){
                answer.add(second.get(s));
                s++;
            }

            else if(first.get(f).compareTo(second.get(s)) < 0){
                answer.add(first.get(f));
                f++;
            }
        }

        else if(f == first.size()){
            while(s != second.size()){
                answer.add(second.get(s));
                s++;
            }
        }

        else{
            while(f != first.size()){
                answer.add(first.get(f));
                f++;
            }
        }
    }