所以,我的計算機科學老師告訴我,除了copyPartArray之外,這裏的每個方法都是無效的。我不知道如何做到這一點,當我嘗試時,排序完全失敗。無效合併排序方法java
public static ArrayList<String> mergeSortHelper(ArrayList<String> a) {
int mid = a.size()/2 - 1;
if (a.size() <= 1)
return a;
return merge(mergeSortHelper(copyPartArray(a, 0, mid)),
mergeSortHelper(copyPartArray(a, mid + 1, a.size() - 1)));
}
public static void mergeSort(ArrayList<String> a) {
ArrayList<String> x = mergeSortHelper(a);
for (int i = 0; i < a.size(); i++) {
a.set(i, x.get(i));
}
}
public static ArrayList<String> merge(ArrayList<String> a,
ArrayList<String> b) {
ArrayList<String> x = new ArrayList<String>(a.size() + b.size());
int aCount = 0;
int bCount = 0;
for (int i = 0; i < a.size() + b.size(); i++) {
if (aCount > a.size() - 1) {
for (int j = bCount; j < b.size(); j++) {
x.add(b.get(j));
}
break;
}
if (bCount > b.size() - 1) {
for (int j = aCount; j < a.size(); j++) {
x.add(a.get(j));
}
break;
}
if ((a.get(aCount)).compareTo(b.get(bCount)) < 0) {
x.add(a.get(aCount));
aCount++;
} else {
x.add(b.get(bCount));
bCount++;
}
}
return x;
}
public static ArrayList<String> copyPartArray(ArrayList<String> a, int s,
int e) {
ArrayList<String> x = new ArrayList<String>();
for (int i = s; i <= e; i++) {
x.add(a.get(i));
}
return x;
我已經試過我的歸併更改爲:
public static void mergeSort(ArrayList<String> a) {
int mid = a.size()/2 - 1;
if (a.size() <= 1)
return;
mergeSort(copyPartArray(a, 0, mid));
mergeSort(copyPartArray(a, mid + 1, a.size() - 1));
merge(a, copyPartArray(a, 0, mid),
copyPartArray(a, mid + 1, a.size() - 1));
}
和擺脫mergeSortHelper的一起。
現在我有:
public static void mergeSort(ArrayList<String> a, int start, int end) {
int mid = (start + end)/2;
if (a.size() <= 1)
return;
mergeSort(a, start, mid);
mergeSort(a, mid + 1, end);
我如何將納入我的合併方法到這一點?
你的老師是殺害不變性:( – 2013-03-04 03:41:10