Question

我目前正在做家庭作业，目标是只递归（没有循环）。我很确定我可以重载并添加辅助方法，这是我看到自己完成此任务的唯一方法。

所以问题是，我有一个int数组A = {1,2,3,4}（或类似的东西），我需要用{10,9,7,4}生成一个返回的数组

10 = 1 + 2 + 3 + 4

9 = 2 + 3 + 4

7 = 3 + 4

4 = 4

我想过使用这样的东西（不是工作代码）

int counter = 0;
public int[] r(int[] numbers){
    return r(number, counter);
}

public int[] r(int[] numbers, int index){
    int sum = 0;
    // base case to check if next value exists otherwise end it

    // this would be a helper method instead of a for loop
    for(int x=index; x<numbers.length; x++){
        sum += numbers[x];
    }

    numbers[index] = sum;
    index++;
    return r(numbers, index);
}

然而，我不知道如何去做。这也是我递归的第一周，所以这对我来说有点混乱。我得到了正确的数组，但我对数字[index] = sum有一个ArrayIndexOutOfBoundsException，在我的return语句上返回r（数字，索引），我不知道如何修复它。有什么想法吗？

Answer 1

您需要一个停止条件，以及之后检索数组的方法

public int sum(int old, int[] numbers, int index) {
    if (index == numbers.length) return old;
    return sum(numbers[index] + old, numbers, index + 1);
}

public int[] r(int[] numbers, int[] output, int count) {
    if (count == numbers.length) {
        return output;
    } else {
        output[count] = sum(0, numbers, 0);
        return r(numbers, output, count + 1);
    }
}

public int[] r(int[] numbers) {
    return r(numbers, new int[numbers.length], 0);
}

编辑：更改了代码，无需for循环

Answer 2

我认为这会给你正确答案：

public static int[] slideAndSumArrayElements(int[] array, int[] result, int index) {
    // base case - stop when the index is same as the array.length
    if (index == array.length) {
        return result;
    } 
    else {
        // Add all elements of the array starting from the index position till length of the array and store the result in result[index]
        result[index] = addArrayElementsRecursively(array, index);

        // slide the main array by incrementing the index 
        return slideAndSumArrayElements(array, result, index + 1);
    }
}

public static int addArrayElementsRecursively(int[] arr, int index){
    // base case - when the index is same as the original array len stop
    if (arr.length == index){
        return 0;
    }

    // add progressively each element of the given array 
    return arr[index] + addArrayElementsRecursively(arr, index + 1);
}

public static void arraySum(){
    int[] array = {1, 2, 3, 4};
    int[] result = new int[array.length];

    result = slideAndSumArrayElements(array, result, 0);
}

输出数组或结果将是： [10,9,7,4]

Answer 3

你的功能是incorect

public int[] r(int[] numbers, int index){

    //--> needs a stop condition e.g. index==numbers.length, index==0

    int sum = 0;
    // base case to check if next value exists otherwise end it

    // this would be a helper method instead of a for loop
    for(int x=index; x<numbers.length; x++){
        //--> numbers has been overwritten by the sum 
        // you should just do numbers[index] = numbers[index-1]+numbers[index]
        // this is opposite to the summation you wish for which starts adding 
        // from the last position
        sum += numbers[x];
    }


    numbers[index] = sum;
    index++;
    return r(numbers, index);
}

你的功能的正确解决方案是

public int[] r(int[] numbers, int index){

    if (index == 0) {
          return numbers;
    }else{
        numbers[index] = numbers[index+1] + numbers[index]
        return r(numbers,index-1);
    }

    public int[] r(int[] numbers){
        return r(numbers, numbers.length);
    }

但是你因为覆盖它而丢失了初始数组

OR

你可以建立一个这样的功能

public int sumRecursive(int[] input, int[] output,int pos){
    if (pos==0){
        output[pos] = input[pos]
        return input[pos]
    }else{
        output[pos] = input[pos] + sumRecursive(input,output,pos-1);
        return output[pos];
     }
}

你需要像这样称呼它

int[] output = new int[input.length];
sumRecursive(input,output,input.length);

增加索引后如何递归添加？

3 个答案: