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我正在使用堆的算法來創建一個包含列表的每個排列的列表列表。每個排列都將是它自己的列表。它在算法中打印時正常工作,但當我嘗試將它添加到列表清單並且它們都是相同的數組(4,1,2,3)時,它無法正常工作。我評論了我測試過的圖片,以確保它能夠正常工作。列表列表中堆的算法實現
我當前的代碼:
public static ArrayList<int[]> lists = new ArrayList<>();
public static void main(String[] args) {
int[] list = {1,2,3,4};
heapsAlgorithm(4,list);
for(int i = 1; i <= lists.size(); i++) {
System.out.println("List " + i + ": " + Arrays.toString(lists.get(i-1)));
}
}
public static void heapsAlgorithm(int n, int[] list) {
if (n == 1) {
lists.add(list);
//System.out.println(Arrays.toString(list));
}
else {
for(int i = 0; i < n; i++) {
heapsAlgorithm(n - 1, list);
if (n % 2 == 0) {
int swap = list[i];
list[i] = list[n-1];
list[n-1] = swap;
}
else {
int swap = list[0];
list[0] = list[n-1];
list[n-1] = swap;
}
}
}
}
工作:
[1, 2, 3, 4]
[2, 1, 3, 4]
[3, 1, 2, 4]
[1, 3, 2, 4]
[2, 3, 1, 4]
[3, 2, 1, 4]
[4, 2, 3, 1]
[2, 4, 3, 1]
[3, 4, 2, 1]
[4, 3, 2, 1]
[2, 3, 4, 1]
[3, 2, 4, 1]
[4, 1, 3, 2]
[1, 4, 3, 2]
[3, 4, 1, 2]
[4, 3, 1, 2]
[1, 3, 4, 2]
[3, 1, 4, 2]
[4, 1, 2, 3]
[1, 4, 2, 3]
[2, 4, 1, 3]
[4, 2, 1, 3]
[1, 2, 4, 3]
[2, 1, 4, 3]
不正確的輸出:
List 1: [4, 1, 2, 3]
List 2: [4, 1, 2, 3]
List 3: [4, 1, 2, 3]
List 4: [4, 1, 2, 3]
List 5: [4, 1, 2, 3]
List 6: [4, 1, 2, 3]
List 7: [4, 1, 2, 3]
List 8: [4, 1, 2, 3]
List 9: [4, 1, 2, 3]
List 10: [4, 1, 2, 3]
List 11: [4, 1, 2, 3]
List 12: [4, 1, 2, 3]
List 13: [4, 1, 2, 3]
List 14: [4, 1, 2, 3]
List 15: [4, 1, 2, 3]
List 16: [4, 1, 2, 3]
List 17: [4, 1, 2, 3]
List 18: [4, 1, 2, 3]
List 19: [4, 1, 2, 3]
List 20: [4, 1, 2, 3]
List 21: [4, 1, 2, 3]
List 22: [4, 1, 2, 3]
List 23: [4, 1, 2, 3]
List 24: [4, 1, 2, 3]
我以爲我用我的ArrayList錯了,但我不知道在哪裏。有什麼建議麼?
您需要將數組副本添加到列表中:'lists.add(Arrays.copyOf(list,list.length))'。 –
謝謝!這工作。爲什麼添加數組副本的原因是什麼,而不是直接添加數組? –
因爲向列表中添加數組(或其他任何內容)不會複製它:您只是存儲引用。因此,對列表「外部」的數組的任何更新也將更新到列表中的「內部」相同的數組。 –