Java program to expand a String if range is given?

Last Updated : 29 Jul, 2022

Suppose we have given a string in which some ranges as specified and we have to place the numbers which is between the given range in the specified place as provided and depicted in the illustration below as follows for a better understanding.

Illustration:

Input  : string x = "1-5, 8, 11-14, 18, 20, 26-29" 
Output : string y = "1, 2, 3, 4, 5, 8, 11, 12, 
                    13, 14, 18, 20, 26, 27, 28, 29"

Approach:

In order to solve the above problem, we can follow the below approach:

First, we have to split the String into String[] array. We have to split the String where we found - symbol.
Now we have a String[] array with the elements. Now we just go to the first index last element i.e. 1 and the preceding index first element of the String[] array say it be 5.
After that with the help of for loop, we can add the numbers which are between 1 and 5 and store them in the String variable.
The above process continues till the length of the string array.

Note:

With the help of Collections and various utility methods we can solve the problem easily but the Collections concept is not a good option performance-wise. If we go through Collections, performance is reduced and time complexity is also increased. There in the below program we explicitly define our own split method and logic.

Implementation: Here we will now be proposing and discussing all three scenarios with help of a clean java program as follows:

Example 1:

Java

// Java program to Expand a String if Range is Given

// Main class
public class Solution {

    // Main driver method
    public static void expand(String word)
    {

        // Creating an object of StringBuffer class to
        // make a modifiable string object
        StringBuilder sb = new StringBuilder();

        // Get all intervals
        String[] strArr = word.split(", ");

        // Traverse through every interval
        for (int i = 0; i < strArr.length; i++) {

            // Get lower and upper
            String[] a = strArr[i].split("-");

            // Setting high and low counters
            if (a.length == 2) {

                int low = Integer.parseInt(a[0]);
                int high
                    = Integer.parseInt(a[a.length - 1]);

                // Condition check holds true
                // Till low counter is lesser or equal to
                // high counter
                while (low <= high) {

                    // Append all numbers
                    sb.append(low + " ");
                    low++;
                }
            }

            // If we reaches here then
            // High counter exceeds lower counter
            else {

                sb.append(strArr[i] + " ");
            }
        }

        // Print the modifiable string
        System.out.println(sb.toString());
    }

    // Method 2
    // Main driver method
    public static void main(String args[])
    {
        // Custom input string as input
        String s = "1-5, 8, 11-14, 18, 20, 26-29";
        expand(s);
    }
}

Output:

1 2 3 4 5 8 11 12 13 14 18 20 26 27 28 29

Example 2:

Java

// Java Program to Illustrate Expansion of String

// Main class
public class StringExpand {

    // Method 1
    // To split the string
    static String[] split(String st)
    {
        // Count how many words in our string
        // Irrespective of spaces
        int wc = countWords(st);
        String w[] = new String[wc];
        char[] c = st.toCharArray();
        int k = 0;

        for (int i = 0; i < c.length; i++) {

            // Initially declaring and initializing
            // string as empty
            String s = "";

            // Whenever we found an non-space character
            while (i < c.length && c[i] != ' ') {

                // Concat with the String s
                // Increment the value of i
                s = s + c[i];
                i++;
            }

            // If the String is not empty
            if (s.length() != 0) {

                // Add the String to the String[]
                // array
                w[k] = s;
                k++;
            }
        }

        // Returning the string array
        return w;
    }

    // Method 2
    // To count the number of words in a string
    static int countWords(String str)
    {
        int count = 0;
        for (int i = 0; i < str.length(); i++) {

            // The below condition to check
            // whether the first character is
            // space or not
            if (i == 0 && str.charAt(i) != ' '
                || str.charAt(i) != ' '
                       && str.charAt(i - 1) == ' ') {
                count++;
            }
        }

        // Returning the count
        return count;
    }

    // Method 3
    // To expand the string
    public static void expand(String s)
    {
        String p = s;
        String[] arr = p.split("\\-");
        String k = "";

        // Traversing over array using for loop
        for (int i = 0; i < arr.length; i++) {

            // Case 1
            if (i != arr.length - 1) {

                String[] arr1 = arr[i].split(", ");
                String[] arr2 = arr[i + 1].split(", ");

                int a = Integer.parseInt(
                    arr1[arr1.length - 1]);
                int b = Integer.parseInt(arr2[0]);

                for (int j = a + 1; j < b; j++) {
                    arr[i] = arr[i] + ", " + j;
                }
            }

            // Case 2
            if (k != "")
                k = k + ", " + arr[i];

            // Case 3
            else
                k = k + arr[i];
        }

        // Print the expanded string
        System.out.println(k);
    }

    // Method 4
    // Main driver method
    public static void main(String[] args)
    {
        // Custom string input
        String s = "1-5, 8, 11-14, 18, 20, 26-29";

        // Calling the method 3 to
        // expand the string
        expand(s);
    }
}

Output:

1, 2, 3, 4, 5, 8, 11, 12, 13, 14, 18, 20, 26, 27, 28, 29

Example 3: