我是一名AP计算机科学专业的学生,我目前的任务是必须制作一个程序,该程序需要一个数字ArrayList,并且只使用标准Java API,使用合并分类。没有任何编译错误,但在运行时它甚至不返回ArrayList!经过一些调试,我发现它没有填充原始列表。请帮忙!代码:Java算法 - 使用ArrayList进行合并排序
import java.io.*;
import java.util.*;
public class MergeSort {
public static void main(String[] args) throws IOException{
Scanner in = new Scanner(System.in);
Random r = new Random();
int size, largestInt, holder;
System.out.println("How many integers would you like me to create?");
size = in.nextInt();
ArrayList<Integer>list = new ArrayList<Integer>(size);
System.out.println("What would the largest integer be?");
largestInt = in.nextInt();
for(int i = 0; i < list.size(); i++){
holder = r.nextInt(largestInt + 1);
list.add(holder);
}
mergeSort(list);
for (int j = 0; j < list.size(); j++) {
if(j == 19 || j == 39 || j == 59 || j == 79 || j == 99 || j == 119 || j == 139 || j == 159 || j == 179 || j == 199){
System.out.print(list.get(j));
System.out.println();
}
else{
System.out.println(list.get(j) + "\t");
}
}
}
static void mergeSort(ArrayList<Integer> list) {
if (list.size() > 1) {
int q = list.size()/2;
ArrayList<Integer> leftList = new ArrayList<Integer>();
for(int i = 0; i > 0 && i <= q; i++){
leftList.add(list.get(i));
}
ArrayList<Integer> rightList = new ArrayList<Integer>();
for(int j = 0; j > q && j < list.size(); j++){
rightList.add(list.get(j));
}
mergeSort(leftList);
mergeSort(rightList);
merge(list,leftList,rightList);
}
}
static void merge(ArrayList<Integer> a, ArrayList<Integer> l, ArrayList<Integer> r) {
int totElem = l.size() + r.size();
int i,li,ri;
i = li = ri = 0;
while (i < totElem) {
if ((li < l.size()) && (ri<r.size())) {
if (l.get(li) < r.get(ri)) {
a.set(i, l.get(li));
i++;
li++;
}
else {
a.set(i, r.get(ri));
i++;
ri++;
}
}
else {
if (li >= l.size()) {
while (ri < r.size()) {
a.set(i, r.get(ri));
i++;
ri++;
}
}
if (ri >= r.size()) {
while (li < l.size()) {
a.set(i, l.get(li));
li++;
i++;
}
}
}
}
}
不必要的循环会损害性能。尝试使用ArrayList.subList(int fromIndex,int toIndex),在ArrayList的情况下应该更快。 –
啊,是的。我忘了ArrayList继承了这个。我一定会改变这一点。谢谢。 –