CODEWITHSUNDEEP
javaarrays
Thev
Thev

Reputation: 1125

Fast way to declare incremental elements of array - Java

Say I have 10 integer variables, x1 to x10.

I have an integer array, as follows:

Int[] countup = new Int[10];

I would like to specify the elements of the array as follows:

countup[0] = x1;
countup[1] = x1 + x2;
countup[2] = x1 + x2 + x3;

And so on until countup[9] is the sum of x1 to x10.

I could do this manually if it was just 10 elements, but in the actual program I'm writing, there's over 100 elements of the array. Is there any way to set the variables of this array quickly?

Upvotes: 0

Views: 191

Answers (3)

Honinbo Shusaku
Honinbo Shusaku

Reputation: 1511

I wanted to find a way to do it in Java 8, and the other answer is probably better:

Here's what I have, but it seems redundant and a waste of time, but I'm unfamiliar with Java 8:

public static void main(String[] args) {
        int[] arr = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
        int length = arr.length;
        for (int i = 1; i < length; i++) {
            System.out.println(Arrays.toString(Arrays.copyOfRange(arr, 0, i + 1)));
            arr[i] = Arrays.stream(Arrays.copyOfRange(arr, 0, i + 1)).sum();
        }
        System.out.println(Arrays.toString(arr));

    }

arr[9] is [1, 3, 7, 15, 31, 63, 127, 255, 511, 1023]

I believe I also interpreted the question differently. I think he wanted in index[i] the sum of all previous elements.

If my interpretation of your question is correct, to do it without Java 8, using 2 loops:

int[] array = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    int length = array.length;
    for(int i = 1; i < length; i++) {
        int sumSoFar = 0;
        for(int j = 0; j <= i; j ++) {
            sumSoFar += array[j];
        }
        array[i] = sumSoFar;
    }

Upvotes: 1

user3103162
user3103162

Reputation: 11

Succinctly:

int[] xNums = { /*your x numbers here*/ };
int[] resultArray = new int[xNums.length];
for(int n = 0; n < xNums.length; n++)
{
for(int i = 0; i <= n; i++)
{
    resultArray[n]+=xNums[i];
}
}

Hope that makes sense!

Upvotes: 1

Shadow
Shadow

Reputation: 4016

A for loop is your best bet, simply put your 10 (or 100) integers into an array of it's own, then loop over your second array referencing indexes of the first array:

int[] xNumbers = { x1, x2, x3, ... x10 };
int[] countup = new int[10];

//Set the 0 index so we don't have to do extra check inside the for loop
//for out-of-bounds exception
countup[0] = xNumbers[0];
for (int i = 1; i < 10; i++) {
    //countup[i-1] is why we set index 0 outside of the loop
    countup[i] = xNumbers[i] + countup[i-1];
}

since countup[i-1] is the sum of the previous numbers, the previous additions are already done for you. In case you don't know what a for loop is, more information can be found here

Upvotes: 4

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