Java split array into ranges

Question

Using Java, I want to split an array of ints into an array of ranges. For example, the array

[1, 2, 3, 4, 5, 6, 7, 8, 100, 101, 102, 103]

would return

[Range(1, 8), Range(100, 103)]

because it consists of 1 to 8 and 100 to 103

It would be best if there were a library, but any sort of method of this conversion is fine.

where is 2 from old array??? if you want random elements from your array then you should write your own method. — Prashant
– Prashant, Commented May 23, 2015 at 16:16
i didn't downvote your question. and how you are pretty sure that i have downvote???? — Prashant
– Prashant, Commented May 23, 2015 at 21:51

Suspended · Accepted Answer · 2015-05-24 22:51:24Z

2

Ok James, here's your working solution :)

private void executeTestCode(){
    int[] arr = new int[]{1, 2, 3, 4, 5, 6, 7, 8, 100, 101, 102, 103};      
    Range[] ranges = Arrays.stream(getRanges(arr)).filter(r -> r != null).toArray(Range[]::new);        
    String output = Arrays.stream(ranges)
            .map(Range::toString)
            .reduce("[", (dynamicString, stringedRange) -> (dynamicString + stringedRange + ", "));
    output = output.substring(0, output.length()-2) + "]";
    System.out.println(output);
}

OUTPUT:
[Range(1, 8), Range(100, 103)]

private Range[] getRanges(int[] toBeProcessed){
    Range[] result = new Range[toBeProcessed.length]; //larger array won't be needed
    int startRange = toBeProcessed[0];  
    int ranges = 0;
    for(int a=0; a<toBeProcessed.length; a++){
        try{
            if(toBeProcessed[a] + 1 != toBeProcessed[a+1]){                 
                result[ranges] = new Range(startRange, toBeProcessed[a]);
                startRange = toBeProcessed[a+1];
                ranges++;
            }                   
        }catch(ArrayIndexOutOfBoundsException e){
            result[ranges] = new Range(startRange, toBeProcessed[toBeProcessed.length-1]);
        }
    }
    return result;      
}

CLASS Range:

class Range{
    private int start, end;
    public Range(int st, int en){
        start = st;
        end = en;
    }

    @Override
    public String toString(){
        return "Range(" +start+ ", " +end+ ")";
    }
}

edited May 24, 2015 at 22:51

answered May 23, 2015 at 20:53

Suspended

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1 Comment

Dean J Over a year ago

I'd give this an upvote, but this is almost certainly a homework question. :-) For things that look like homework, it's (sometimes) favored to give hints and not the full answer. That said, good code.

Suspended · Accepted Answer · 2015-05-23 16:13:16Z

1

You can use

Arrays.copyOfRange(yourArray, inclusiveStartIndex, exclusiveEndIndex);

It returns new array.

answered May 23, 2015 at 16:13

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2 Comments

Dean J Over a year ago

Why isn't it what you want? That seems like what you asked for here, so it's hard to suggest something else until folks know why this doesn't work. :)

Dean J Over a year ago

More specifically, arrays in Java are immutable; they can't be changed once created. (The values in them can, but the array itself - including it's length - is permanent.) There's not a way to split arrays without at least doing a shallow copy of primatives stored in them. (If your values were Integer instead of int, a shallow copy could use existing Objects.)

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