我基本上尝试使用递归并创建一个小程序，找到10个项目中的0-10个所有组合（{1 apple，0 grapes}，{2 apple，0 grape}，{0 apple， 1葡萄}等。）。
import java.util.Arrays;
import java.util.List;
public class main {
public static void main(String[] args) {
System.out.println("Starting..");
long startTime = System.currentTimeMillis();
List<Integer> list_to_start = Arrays.asList(new Integer[] {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0});
String[] name_of_list_to_start = new String[] {"Grapes", "Strawberries", "Raspberries", "Blackberries", "Pineapples", "Oranges", "Prunes", "Pears", "cherries", "Peaches", "Apples"};
System.out.println(list_to_start.size());
counter(list_to_start.size(), list_to_start, name_of_list_to_start);
long endTime = System.currentTimeMillis();
System.out.println("Total execution time: " + (endTime-startTime));
}
private static void counter(int length, List<Integer> list_to_start, String[] name_of_list_to_start) {
// If we've gone through everything then return the results
if (length == 0) {
for (int i = 0; i<list_to_start.size(); i++) {
//System.out.println(name_of_list_to_start[i] + " = " + list_to_start.get(i));
}
//System.out.println("****");
return;
}
//This part basically increments list_to_start and then the above part displays it.
for (int i = 0; i<=10; i++) {
if (length != 0 ) {
list_to_start.set((length-1), i);
counter((length-1), list_to_start, name_of_list_to_start);
list_to_start.set((length-1), 0);
}
}
}
}
现在它有10,000,000,000个循环（10 ^ 10）所以我理解为什么需要很长时间，但我想知道是否有任何Java或算法技巧可以用来减少循环次数来加速它？
我曾想过使用线程/多处理，但是仍然需要进行相同数量的循环，这仍然需要很长时间。我不确定这里是否有任何数据结构，排序算法或缓存算法。或者我可以将结果并行添加到数组中，然后将它们组合在一起以获得最终结果吗？我不熟悉任何其他现有方法，因此非常欢迎任何语言特定技巧或算法解决方案的建议。
更新：为了澄清我正在做什么以及性能，我将发布几个例子。要增加处理时间，只需在list_to_start中添加/删除零（以下结果以毫秒为单位）：
1 zero = 0
2 zero = 1
3 zero = 1
4 zero = 29
5 zero = 37
6 zero = 115
7 zero = 345
8 zero = 1517
9 zero = 23738 (23 seconds)
10 zero = over 30 min. I gave up.
输出（我禁用它使其运行得更快）是2个变量（上面的代码运行10）：
Grapes = 0
Strawberries = 0
****
Grapes = 1
Strawberries = 0
****
Grapes = 2
Strawberries = 0
****
Grapes = 3
Strawberries = 0
****
Grapes = 4
Strawberries = 0
****
Grapes = 5
Strawberries = 0
****
Grapes = 6
Strawberries = 0
****
Grapes = 7
Strawberries = 0
****
Grapes = 8
Strawberries = 0
****
Grapes = 9
Strawberries = 0
****
Grapes = 10
Strawberries = 0
****
Grapes = 0
Strawberries = 1
****
Grapes = 1
Strawberries = 1
****
Grapes = 2
Strawberries = 1
****
Grapes = 3
Strawberries = 1
****
Grapes = 4
Strawberries = 1
****
Grapes = 5
Strawberries = 1
****
Grapes = 6
Strawberries = 1
****
Grapes = 7
Strawberries = 1
****
Grapes = 8
Strawberries = 1
****
Grapes = 9
Strawberries = 1
****
Grapes = 10
Strawberries = 1
****
Grapes = 0
Strawberries = 2
****
Grapes = 1
Strawberries = 2
****
Grapes = 2
Strawberries = 2
****
Grapes = 3
Strawberries = 2
****
Grapes = 4
Strawberries = 2
****
Grapes = 5
Strawberries = 2
****
Grapes = 6
Strawberries = 2
****
Grapes = 7
Strawberries = 2
****
Grapes = 8
Strawberries = 2
****
Grapes = 9
Strawberries = 2
****
Grapes = 10
Strawberries = 2
****
Grapes = 0
Strawberries = 3
****
Grapes = 1
Strawberries = 3
****
Grapes = 2
Strawberries = 3
****
Grapes = 3
Strawberries = 3
****
Grapes = 4
Strawberries = 3
****
Grapes = 5
Strawberries = 3
****
Grapes = 6
Strawberries = 3
****
Grapes = 7
Strawberries = 3
****
Grapes = 8
Strawberries = 3
****
Grapes = 9
Strawberries = 3
****
Grapes = 10
Strawberries = 3
****
Grapes = 0
Strawberries = 4
****
Grapes = 1
Strawberries = 4
****
Grapes = 2
Strawberries = 4
****
Grapes = 3
Strawberries = 4
****
Grapes = 4
Strawberries = 4
****
Grapes = 5
Strawberries = 4
****
Grapes = 6
Strawberries = 4
****
Grapes = 7
Strawberries = 4
****
Grapes = 8
Strawberries = 4
****
Grapes = 9
Strawberries = 4
****
Grapes = 10
Strawberries = 4
****
Grapes = 0
Strawberries = 5
****
Grapes = 1
Strawberries = 5
****
Grapes = 2
Strawberries = 5
****
Grapes = 3
Strawberries = 5
****
Grapes = 4
Strawberries = 5
****
Grapes = 5
Strawberries = 5
****
Grapes = 6
Strawberries = 5
****
Grapes = 7
Strawberries = 5
****
Grapes = 8
Strawberries = 5
****
Grapes = 9
Strawberries = 5
****
Grapes = 10
Strawberries = 5
****
Grapes = 0
Strawberries = 6
****
Grapes = 1
Strawberries = 6
****
Grapes = 2
Strawberries = 6
****
Grapes = 3
Strawberries = 6
****
Grapes = 4
Strawberries = 6
****
Grapes = 5
Strawberries = 6
****
Grapes = 6
Strawberries = 6
****
Grapes = 7
Strawberries = 6
****
Grapes = 8
Strawberries = 6
****
Grapes = 9
Strawberries = 6
****
Grapes = 10
Strawberries = 6
****
Grapes = 0
Strawberries = 7
****
Grapes = 1
Strawberries = 7
****
Grapes = 2
Strawberries = 7
****
Grapes = 3
Strawberries = 7
****
Grapes = 4
Strawberries = 7
****
Grapes = 5
Strawberries = 7
****
Grapes = 6
Strawberries = 7
****
Grapes = 7
Strawberries = 7
****
Grapes = 8
Strawberries = 7
****
Grapes = 9
Strawberries = 7
****
Grapes = 10
Strawberries = 7
****
Grapes = 0
Strawberries = 8
****
Grapes = 1
Strawberries = 8
****
Grapes = 2
Strawberries = 8
****
Grapes = 3
Strawberries = 8
****
Grapes = 4
Strawberries = 8
****
Grapes = 5
Strawberries = 8
****
Grapes = 6
Strawberries = 8
****
Grapes = 7
Strawberries = 8
****
Grapes = 8
Strawberries = 8
****
Grapes = 9
Strawberries = 8
****
Grapes = 10
Strawberries = 8
****
Grapes = 0
Strawberries = 9
****
Grapes = 1
Strawberries = 9
****
Grapes = 2
Strawberries = 9
****
Grapes = 3
Strawberries = 9
****
Grapes = 4
Strawberries = 9
****
Grapes = 5
Strawberries = 9
****
Grapes = 6
Strawberries = 9
****
Grapes = 7
Strawberries = 9
****
Grapes = 8
Strawberries = 9
****
Grapes = 9
Strawberries = 9
****
Grapes = 10
Strawberries = 9
****
Grapes = 0
Strawberries = 10
****
Grapes = 1
Strawberries = 10
****
Grapes = 2
Strawberries = 10
****
Grapes = 3
Strawberries = 10
****
Grapes = 4
Strawberries = 10
****
Grapes = 5
Strawberries = 10
****
Grapes = 6
Strawberries = 10
****
Grapes = 7
Strawberries = 10
****
Grapes = 8
Strawberries = 10
****
Grapes = 9
Strawberries = 10
****
Grapes = 10
Strawberries = 10
答案 0 :(得分：3)
您可以使用单个循环。
有11 ^ 10种可能的组合。你可以遍历所有
// String[] names = "Grapes,Strawberries,Raspberries,Blackberries,Pineapples,Oranges,Prunes,Pears,Cherries,Peaches,Apples".split(",");
String[] names = "Pineapples,Oranges,Prunes,Pears,Cherries,Peaches,Apples".split(",");
int maxQuantity = 10;
long combinations = 1;
int quantities = maxQuantity + 1;
for (String _ : names)
combinations *= quantities;
long start = System.currentTimeMillis();
PrintStream out = new PrintStream(new BufferedOutputStream(new FileOutputStream("combinations.tsv")));
// heading
for (String name : names)
out.print(name + "\t");
out.println();
for (long comb = 0; comb < combinations; comb++) {
// comb is a base N number of digits 0 to maxQuantity.
long c = comb;
for (int i = 0; i < names.length; i++) {
long n = c % quantities;
c /= quantities;
out.print(n);
out.print('\t');
}
out.println();
}
out.close();
System.out.println("Took " + (System.currentTimeMillis() - start) / 1e3 + " seconds" +
" to write " + combinations + " combinations");
打印
Took 51.585 seconds to write 19487171 combinations
如果您注释掉这些行，则会将值打印到您获得的文件
Took 0.065 seconds to write 19487171 combinations
注意：此程序将花费大部分时间进行打印。如果您取下打印部件，它将很快完成。 ;）
答案 1 :(得分：0)
假设你只关心同一个项目的第一个实例，你可以在匹配时打破循环以避免额外的循环。你能否更好地分解这里的'问题'（你的计划应该做什么）？