How do you add all elements in an 2d array, circularly?

Question

Given an 2d array of strings how to I add up all the elements so that each index in the array is the sum of the rest of the array? For example with an array [[a], [b], [c], [d], [e]] I end up with
[[a+b+c+d+e], [a+b+c+d+e], [a+b+c+d+e], [a+b+c+d+e],[a+b+c+d+e]] . I guess it doesn't have to be a 2d array it can be a 1d array of string and I end up with a string "a+b+c+d+e" in every index. When I say circularly I mean with loops, no extra memory space. So maybe after the first iteration it could look something like [[a], [a + b], [a+b+c], [a+b+c+d], [a+b+c+d+e]] . What would the code for something like this be? The answer can be is psuedocode or any language

something like this: https://andrew.gibiansky.com/blog/machine-learning/baidu-allreduce/

Answer 1

I'm not quite sure what you want to achieve. But it might be worthwhile if you look at Arrays#parallelPrefix , which you can use to cumulate the single elements of an array.

public static void main(String[] args) {
    String[] str = {"a","b","c","d","e"};
    Arrays.parallelPrefix(str, (s1,s2) -> s1+s2);
    System.out.println(Arrays.toString(str));
}

//[a, ab, abc, abcd, abcde]

Answer 2

You can get such string by adding all elements to one of the items and then copying the result to other items.

    String[] arr = new String[] {"a", "b", "c", "d", "e"};

    for(int i = 1; i < arr.length; ++i) {
        arr[0] += arr[i];
    }
    for(int i = 1; i < arr.length; ++i) {
        arr[i] = arr[0];
    }       
    System.out.println(Arrays.toString(arr));

Answer 3

According to your attached link i think below solution will help you:

        int n = 5, i, j;
        String[][] gpu = new String[n][n];
        //here generate initial gpu....
        for (i = 0; i < n; i++) {
            for (j = 0; j < n; j++) {
                char ch = (char) (97 + j);
                gpu[i][j] = ""+ch+i;
            }
        }
        System.out.println("Initial Gpu: ");
        for (i = 0; i < n; i++) {
            for (j = 0; j < n; j++) {
                System.out.print(gpu[i][j] + "|");
            }
            System.out.println();
        }
        // here calculated your expected logic
        for (i = 0; i < n-1; i++) {
            for (j = 0; j < n; j++) {
                gpu[(i+j+1)%n][j] = gpu[(i+j)%n][j] + gpu[(i+j+1)%n][j];
            }
        }
        System.out.println("Final Gpu: ");
        for (i = 0; i < n; i++) {
            System.out.print(gpu[n-1][i] + "|");
        }
        System.out.println();