Split String when character changes. Possible Regex solution? [duplicate]

Question

I have some Strings consisting of only digits, and I want to split it whenever the character changes.

For example:

• "11101100112021120" goes to: {"111", "11", "11", "2", "2", "11", "2"}
• "222222222" goes to {"222222222"}
• "222222122" goes to {"222222", "1", "22"}
• "000000000" goes to {}
• "0000100000" goes to {"1"}
• "11121222212112133321" goes to {"111", "2", "1", "2222", "1", "2", "11", "2", "1", "333", "2", "1"}

I want a nice way to do this.

I know two ways to go about this: just brute forcing, or adding section by section. Or, I could go through and remove all 0's and replace with a 0, then add 0's when characters change, and then just do a split on 0's, but both of those ways just look dumb. If anyone has any idea on a better/prettier way to do this, regex or logic, it'd be nice.

Answer 1

This seems to work like you expect

data.split("0+|(?<=([1-9]))(?=[1-9])(?!\\1)");

Test:

String[] tests = { "11101100112021120", "222222222", "222222122",
        "000000000", "0000100000", "11121222212112133321" };

for (String data : tests) {
    System.out.println(data + " ->" + Arrays.toString(data.split("0+|(?<=([1-9]))(?=[1-9])(?!\\1)")));
    System.out.println("-----------------------");
}

output:

11101100112021120 ->[111, 11, 11, 2, 2, 11, 2]
-----------------------
222222222 ->[222222222]
-----------------------
222222122 ->[222222, 1, 22]
-----------------------
000000000 ->[]
-----------------------
0000100000 ->[, 1]     // <-- only problem - empty first element 
-----------------------
11121222212112133321 ->[111, 2, 1, 2222, 1, 2, 11, 2, 1, 333, 2, 1]
-----------------------

Unfortunately leading zeros will let array to contain additional empty String. To get rid of it you can earlier remove these zeros with data.replaceFirst("^0+(?=[^0])", "")