卡在组合问题 [英] Stuck with Combination Problem

问题描述

我的程序有问题.我已经提取了一组数据，我想测试一下特定数字是否存在组合.例如，我有一个int数组，即1 2 3 4 5，我想知道是否存在7的组合，它必须回答是3 + 4.

I'm having a problem w/ my program. I have extracted a set of data and I would like to test if there is a combination for a particular number. For example, I have an array of int, 1 2 3 4 5, I would like to know if there is a combination for 7 maybe, and it must answer yes there is 3 + 4.

我发现我需要使用组合公式.因此，我认为外循环可能类似于5C1..5C2..5C3..etc，开始先取1"然后取2"，以找出所有可能的组合.问题是我被困在如何在实际代码中实现这一点.

I figured out that I need to use the combination formula. So I thought that the outer loop may go like 5C1..5C2..5C3..etc, starting to "take 1" then "take 2" at a time to find out all the possible combinations. The problem is I'm stuck at how to implement this in actual codes.

我对Math的理解不是很好，定义的循环结构确实会有所帮助.

I'm not really very good with Math, A defined loop structure would really help.

非常感谢！

推荐答案

这里是一种从整数列表中获取所有可能总和的方法:

Here is a method that gets all possible sums from a List of Integers:

public static void getAllPermutations(final List<Integer> data,
    final Set<Integer> holder){

    if(data.isEmpty()){
        return;
    }
    final Integer first = data.get(0);
    if(data.size() > 1){
        getAllPermutations(data.subList(1, data.size()), holder);
        for(final Integer item : new ArrayList<Integer>(holder)){
            holder.add(first.intValue() + item.intValue());
        }
    }
    holder.add(first);
}

用法:

List<Integer> data = Arrays.asList(1, 2, 3, 4, 5, 6);
Set<Integer> permutations = new TreeSet<Integer>();
getAllPermutations(data, permutations);
System.out.println(permutations);

输出:

[1、2、3、4、5、6、7、8、9、10、11、12、13、14、15、16、17、18、19、20、21]

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21]

---

虽然此解决方案不会为您提供导致求和的操作数，但它将包括从1到1 + 2 + 3 + 4 + 5 + 6

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