Appending Integer array elements in Java

Question

I have an array, say

int a[]={2,0,1,0,1,1,0,2,1,1,1,0,1,0,1};

I need to append each of the 5 neighboring elements and assign them to a new array b with length=(a.length/5); and i want to append the 5 neighboring elements so that I have: int b[]={20101,10211,10101}; I need to do this for various length arrays, in most cases with length of a being greater than 15.

Any help would be greatly appreciated, I'm programming in Java.

Thanks in advance.

Answer 1

It's pretty straighforward:

// Assuming a.length % 5 == 0.
int[] b = new int[a.length / 5];
for (int i = 0; i < a.length; i += 5) {
    b[i/5] = a[i]*10000 + a[i+1]*1000 + a[i+2]*100 + a[i+3]*10 + a[i+4];
}

Answer 2

This works with (a.length % 5) != 0, and keeps leading zeroes (by storing digits into String).

    int a[]={2,0,1,0,1,1,0,2,1,1,1,0,1,0,1,0,0,7};

    final int N = 5;
    String b[] = new String[(a.length + N - 1)/ N];
    StringBuilder sb = new StringBuilder(N);
    int x = 0;
    for (int i = 0; i < b.length; i++) {
        sb.setLength(0);
        for (int k = 0; k < N && x < a.length; k++) {
            sb.append(a[x++]);
        }
        b[i] = sb.toString();
    }
    System.out.println(java.util.Arrays.toString(b));
    // prints "[20101, 10211, 10101, 007]"

---

Alternately, you can also use regex:

    String[] arr =
        java.util.Arrays.toString(a)
        .replaceAll("\\D", "")
        .split("(?<=\\G.{5})");
    System.out.println(java.util.Arrays.toString(arr));
    // prints "[20101, 10211, 10101, 007]"

Basically this uses Arrays.toString(int[]) to append all digits into one long String, then removes all non-digits \D, then uses \G-anchored lookbehind to split every .{5}

Answer 3

Naive approach.

import java.util.ArrayList;

/* Naive approach */
public class j2728476 {
    public static void main(String[] args) {
        int a[] = {2,0,1,0,1,1,0,2,1,1,1,0,1,0,1};
        ArrayList<String> al = new ArrayList<String>();
        String s = "";
        for (int i = 0; i < a.length; i++) {
            if (i % 5 == 0 && i != 0) {
                al.add(s);
                s = "" + a[i];
            } else {
                s += a[i];
            }
        }
        al.add(s);
        for (String t : al) {
            // convert values to ints ...
            System.out.println(t);
        }
    }
}

Will print:

20101
10211
10101