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I would like to convert the elements of an array of integers into a single integer. Note that I haven't learn the join or number methods in class yet so they cannot be use for this program.

For example, {1, 2, 3} would become 123.

Here is my thought of process:

  1. Convert the first element of the array into a String
  2. Concatenate the remaining elements
  3. Use Integer.parseInt() to convert the String back to an integer

Can anyone confirm I am doing this the right way or suggest an alternative way?

Also, by curiosity, how could we compare the elements of two integer arrays without using the class Arrays?

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  • Hi, you want to sum them ? Or you want to convert element of integer to string and concatanate them and parse the result value to int ? Commented Mar 11, 2019 at 23:53
  • If the assignment doesn't specify how you need to do this conversion, then there are a few much easier ways to do it. The first one is return 1; - it converts any array to a single integer. The second one links the result to the array to a degree: return array.length;. If your assignment does say how, then you forgot to mention that in your question. Commented Mar 11, 2019 at 23:57
  • @MykhailoMoskura No, I do not want to sum them, just concatenate them. For example, {1, 2, 3} would become 123. Commented Mar 11, 2019 at 23:57
  • 1
    See String::concat. Commented Mar 12, 2019 at 0:00
  • Provide further detail as edits to your Question rather than as Comments. Commented Mar 12, 2019 at 0:04

2 Answers 2

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1

This is how it can be done using java 8: 

 final int[] array = new int[]{1,2,3};
   final String result = IntStream
                    .of(array)
                    .boxed()
                    .map(String::valueOf)
                    .collect(Collectors.joining());
   final int intResult = Integer.parseInt(result);

I also would add check if array contains one element for example 

 public int arrayOfIntsAsSingleInt ( final int[] array){
            if (Objects.isNull(array) || array.length == 0) {
                throw new IllegalArgumentsException("array could not be null or empty")
            } else if (array.length == 1) {
                return array[0];
            }
            return convertArraysofIntAsSingleInt(array);
        }

We can compare two integers by writing custom Comparator or

invoke Integer.compareTo(anotherInteger) method

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7 Comments

I would like to compare the elements inside the array not integers
Why do you need it ? The problem what you want to solve?
I am just curious
What do you mean by inside an array ?
I want to compare the elements inside an array (numbers inside the array) such that {1, 2, 3} and {1, 2, 3} would return true while {4, 5, 6} and {6, 5, 4}
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1

Can anyone confirm I am doing this the right way

If you input is valid,your method is right to do what you want. @Mykhailo Moskura give a method use Java 8 Stream API to join string.

suggest an alternative way?

if you element in your input array within a certain range(0,9) and the first element must not be 0,you can try this code: int[] inputs = {1, 2, 3};

    int factor = 0;
    int result = 0;
    for (int i = 0; i < inputs.length; i++) {
        result = inputs[i] + factor * 10;
        factor = result;
    }

    System.out.println(result);

the output is: 123

compare two array not use Arrays

Assume not use any tool,you can use two map to compare two arrays:

public static boolean compareArray(int[] arr1, int[] arr2) {
        if (arr1.length != arr2.length) {
            return false;
        }

        Map<Integer, Integer> map1 = new HashMap<>();
        Map<Integer, Integer> map2 = new HashMap<>();
        for (int arr : arr1) {
            Integer times = map1.getOrDefault(arr, 0);
            map1.put(arr, times + 1);
        }
        for (int arr : arr2) {
            Integer times = map2.getOrDefault(arr, 0);
            map2.put(arr, times + 1);
        }

        for (Integer key : map1.keySet()) {
            if (!map1.get(key).equals(map2.get(key))) {
                return false;
            }
        }
        return true;
    }
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4 Comments

Hi , it can be done with less code just iterating through array.length and comparing them using index from cycle
compare two arrays:array1={1,2,3,2},array2={2,1,2,3},they are the same array,can we solve this?
Same array is array which have the same order of elements
Not actually O(n) , if would be collision worst case would be like O(n^2) , you have not mentioned this case because big o notation is worst case

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