java—从给定的字符串数组创建多个数组

ia2d9nvy 于 2021-07-12 发布在 Java

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我有一个唯一字符串数组，需要从中创建所有可能的具有相同长度的数组。

String[] str = {"Belgium", "France", "Germany"};

我们的目标是创建一个数组列表，这些数组在每个索引处都有上面数组中所有可能的值，

[Belgium, Belgium, Belgium]
[Belgium, Belgium, France]
[Belgium, Belgium, Germany]
[Belgium, France, Belgium]
[Belgium, France, France]
[Belgium, France, Germany]
[Belgium, Germany, Belgium]
[Belgium, Germany, France]
[Belgium, Germany, Germany]
[France, Belgium, Belgium]

....

[Germany, Germany, France]
[Germany, Germany, Germany]

我创建这个的代码如下

static List<String[]> getAllAllocations(String[] input){
    List<String[]> result = new ArrayList<>();
    if(input.length == 2){
        for(int i = 0; i < 2; i++){
            for(int j = 0; j < 2; j++){
                result.add(new String[]{input[i], input[j]});
            } 
        }
    }
    else if(input.length == 3){
        for(int i = 0; i < 3; i++){
            for(int j = 0; j < 3; j++){
                for(int k = 0; k < 3; k++){
                    result.add(new String[]{input[i], input[j], input[k]});
                }
            } 
        }
    }
    else if(input.length == 4){
        for(int i = 0; i < 4; i++){
            for(int j = 0; j < 4; j++){
                for(int k = 0; k < 4; k++){
                    for(int m = 0; m < 4; m++){
                        result.add(new String[]{input[i], input[j], input[k], input[m]});
                    }
                }
            } 
        }
    }
    //else if(input.length == 5) similar code with 5 for loops
    //else if(input.length == 6) similar code with 6 for loops
    //else if(input.length == 7) similar code with 7 for loops
    //else if(input.length == 8) similar code with 8 for loops
    return result;
}

数组的长度在2到8之间。我如何动态地创建for循环，而不是链接if-else检查或任何其他方法，以一种比我上面做的更好的方式来实现这一点？

Java for-loop Arrays

来源：https://stackoverflow.com/questions/67181677/create-multiple-arrays-from-a-given-string-array

1条答案

按热度按时间

tjrkku2a1#

递归解

public static List<String[]> getAllAllocations(String[] input) {
    List<String[]> result=new ArrayList<String[]>();
    getAllAllocations(result, input, new String[input.length], 0);
    return result;
}

public static void getAllAllocations(List<String[]> result, String[] input, String[] current, int depth) {
    if (depth>=input.length) {
        result.add(current.clone());
    } else {
        for (int i=0;i<input.length;i++) {
            current[depth]=input[i];
            getAllAllocations(result, input, current, depth+1);
        }
    }
}

迭代解法

public static List<String[]> getAllAllocations2(String[] input) {
    List<String[]> result=new ArrayList<String[]>();

    int[] counters=new int[input.length];

    boolean done=false;
    while (!done) {

        String[] comb=new String[input.length];
        for (int i=0;i<comb.length;i++) {
            comb[i]=input[counters[i]];
        }
        result.add(comb);

        done=true;
        for (int i=0;i<counters.length;i++) {
            counters[i]++;
            if (counters[i]>=input.length) {
                counters[i]=0;
            } else {
                done=false;
                break;
            }
        }
    }

    return result;
}

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java—从给定的字符串数组创建多个数组

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