How do I get the last substring starting with +,-,*,/?

Question

If I have expression in a string variable like this 20+567-321, so how can I extract last number 321 from it where operator can be +,-,*,/

If the string expression is just 321, I have to get 321, here there is no operator in the expression

Kaushal28 · Accepted Answer · 2017-09-18T15:26:38.573

4

You can do this by splitting your string based on your operators as following:

String[] result = myString.split("[-+*/]");

[+|-|*|/] is Regex that specifies the points from where your string should be split. Here, result[result.length-1] is your required string.

EDIT As suggested by @ElliotFrisch we need to escape - in regex while specifying it. So following pattern should also work:

String[] result = myString.split("[+|\\-|*|/]");

Here is the list of characters they need to be escaped.

Link.

edited Sep 18 '17 at 15:26

answered Sep 18 '17 at 03:04

Kaushal28

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I needed `String[] result = myString.split("[+|-|*|/]");` – Elliott Frisch Sep 18 '17 at 03:08
for negative sign it is returning incorrect results - for example "87-1" the result is 87-1, but result should be 1 – sjso Sep 18 '17 at 05:20
@raxx Make sure you are using the same character for `-`. You are probably using different characters in the expression and in your code. – Klas Lindbäck Sep 18 '17 at 10:29
@raxx please check now. I've updated the answer. I've tested it and it's working. Here is the link where I've tested it. `jdoodle.com/a/7uQ` – Kaushal28 Sep 18 '17 at 14:45
@ElliottFrisch as per your suggestion your pattern should work in `87-1` but it is giving the same output. Any reasons? – Kaushal28 Sep 18 '17 at 14:48
Interesting; `String[] result = myString.split("[+|\\-|*|/]");` works. – Elliott Frisch Sep 18 '17 at 14:55
Okay so we have to escape `-` here. Thanks – Kaushal28 Sep 18 '17 at 15:14

Saurav Sahu · Answer 2 · 2017-09-18T06:35:04.627

4

This seems to be an assignment for learning programming and algo, and also I doubt splitting using Regex would be efficient in a case where only last substring is required.

Start from end, and iterate until the length of the string times.
Declare a empty string say Result
While looping, if any of those operator is found, return Result, else prepend the traversed character to the string Result.
Return Result

edited Sep 18 '17 at 06:35

answered Sep 18 '17 at 03:07

Saurav Sahu

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score 0 · Answer 3 · answered Sep 18 '17 at 08:56

String[] output = s.split("[+-/*]");
String ans = output[output.length-1];

Assumption here that there will be no spaces and the string contains only numbers and arithmetic operators.

[+-/*] is a regular expression that matches only the characters we provide inside the square brackets. We are splitting based on those characters.

score 0 · Answer 4 · answered Sep 18 '17 at 09:40

If you wanna do it with StringTokenizer:

 public static void main(String args[])

{
   String expression = "20+567-321";
   StringTokenizer tokenizer = new StringTokenizer(expression, "+-*/");
   int count = tokenizer.countTokens();
   if( count > 0){
       for(int i=0; i< count; i++){
           if(i == count - 1 ){
               System.out.println(tokenizer.nextToken());
           }else{
               tokenizer.nextToken();
           }
       }
   } 
}

Recall you can specify multiple delimiters in StringTokenizer.

How do I get the last substring starting with +,-,*,/?

4 Answers4