我是一名AP計算機科學專業的學生,我目前的任務是必須製作一個程序,該程序需要一個數字ArrayList,並且只使用標準Java API,使用合併分類。沒有任何編譯錯誤,但在運行時它甚至不返回ArrayList!經過一些調試,我發現它沒有填充原始列表。請幫忙!代碼:Java算法 - 使用ArrayList進行合併排序
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++;
}
}
}
}
}
不必要的循環會損害性能。嘗試使用ArrayList.subList(int fromIndex,int toIndex),在ArrayList的情況下應該更快。 –
啊,是的。我忘了ArrayList繼承了這個。我一定會改變這一點。謝謝。 –