Is there any way to convert string to 2d matrix in less than or equal to O(nlgn) time?-CodePudding

I have an assignment about divide and conquer which isn't the problem at all; the actual problem is that I can't convert the given string into the 2dimentional array it wants me to. The problem's running time has to be O(nlogn) which is why I can't use multiple loops for this solution. The input string would be something like:

[[0,2,3],[2,5,3] , [1,2022,5] , [2,5,77]]

And I have to put it into a two dimentional array like so. I saw a few question on stackoverflow like this one, but I can't get the solutions right on Java, that's why I asked this question. So here is what I have done by far (which I'm super ashamed of):

   public static void main(String[] args) {
    
    Scanner scan = new Scanner(System.in);
    
    String inputs = scan.nextLine();
    String[] numbers=new String[100];
    int[][] arr;
    
    numbers=inputs.split("[");
    
    for (String is : numbers) {
        System.out.println(is);
    }
    
    boolean flag=false;
    

    
}

I realised the split function does not work like that.It gives me errors.

Would you please help me convert a given string that has a 2d array like template to an actual 2d array?I'd be very thankful if you'd help.

CodePudding user response：

Try this.

String input = "[[0,2,3],[2,5,3] , [1,2022,5] , [2,5,77]]";

int[][] output = Stream.of(input.replaceAll("\\s", "").split("\\],\\["))
    .map(row -> Stream.of(row.replaceAll("[\\[\\]]", "").split(","))
        .mapToInt(e -> Integer.parseInt(e))
        .toArray())
    .toArray(int[][]::new);

System.out.println(Arrays.deepToString(output));

output:

[[0, 2, 3], [2, 5, 3], [1, 2022, 5], [2, 5, 77]]

CodePudding user response：

Some sort of loops would be needed anyway if array is expected because it would be needed to iterate the input string until a closing bracket ] is detected along with counting the number of numbers in the subarray, and then the numbers should be parsed one by one inside the "subarray" substring.

A solution based on the regular expression and Stream API may look like this:

find a match for a subarray
parse separate digits in the substring and create a subarray
create the resulting 2D array

public static int[][] readArray(String str) {
    Pattern pArr = Pattern.compile("\\[\\s*\\]|\\[\\s*([ -]?\\d )(\\s*,\\s*[ -]?\\d )*\\]");
    Pattern pInt = Pattern.compile("[ -]?\\d ");
    return pArr.matcher(str).results()
        .map(arr -> pInt.matcher(arr.group()).results()
                        .map(MatchResult::group)
                        .mapToInt(Integer::parseInt).toArray()
        )
        .toArray(int[][]::new);
}

Test

System.out.println(Arrays.deepToString(readArray(" [[], [0], [-1,  1], [ 1, 2, 3, -10 ]] ")));

[[], [0], [-1, 1], [1, 2, 3, -10]]