[英]Recursive Mergesort in Java
首先,在此先感謝您的所有答復,我們深表感謝。 現在以這篇文章為目的; 我在用Java實現合並排序時遇到麻煩。 我收到了空指針異常,但是,我無法弄清楚錯誤是什么,對我來說代碼看起來還不錯。 到目前為止,這是我所擁有的:
public List mSort(List l) {
if (l.size() <= 1)
return l;
List left = null;
List right = null;
int mid = l.size() / 2;
for (int x = 0; x < mid; x++)
left.add(l.get(x));
for (int x = 0; x >= mid; x++)
right.add(l.get(x));
left = mSort(left);
right = mSort(right);
return merge(left, right);
}
public List merge(List left, List right) {
List r = null;
while (left.size() > 0 || right.size() > 0) {
if (left.size() > 0 && right.size() > 0)
if (left.get(0) <= right.get(0)) {
r.add(left.get(0));
left.remove(0);
}
else {
r.add(right.get(0));
right.remove(0);
}
else if (left.size() > 0) {
r.add(left.get(0));
left.remove(0);
}
else if (right.size() > 0) {
r.add(right.get(0));
right.remove(0);
}
}
return r;
}
...顯然,指針異常來自'mSort'方法中的'For'語句,任何能指出我的錯誤或指導我朝正確方向的東西都將不勝感激!!!
left
和right
為空,您不能添加!!!
List left = new ArrayList();
List right = new ArrayList();
for (int x = 0; x < mid; x++)
left.add(l.get(x));
for (int x = 0; x >= mid; x++)
right.add(l.get(x));
一定是
int x = 0;
for (; x < mid; x++)
left.add(l.get(x));
for (; x < l.size(); x++)
right.add(l.get(x));
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