Split a String into a Number of Substrings in Java (original) (raw)

Last Updated : 17 Feb, 2022

Given a String, the task it to split the String into a number of substrings.

A String in java can be of 0 or more characters.

Examples :

(a) "" is a String in java with 0 character (b) "d" is a String in java with 1 character (c) "This is a sentence." is a string with 19 characters.

Substring: A String that is a part of another string is called substring of the other string.

Example 1: Let us consider the string bat. The possible substrings are:

(1) "b" (2) "ba" (3) "bat", every string is a substring of itself (4) "a" (5) "at" (6) "t" (7) "" , "" is a substring of every string

Example 2: Let us consider the string The Cat. The possible substrings are:

(1) "T" (2) "Th" (3) "The" (4) "The " (5) "The C" (6) "The Ca" (7) "The Cat", every string is a substring of itself (8) "h" (9) "he" (10) "he " (11) "he C" (12) "he Ca" (13) "he Cat" (14) "e" (15) "e " (16) "e C" (17) "e Ca" (18) "e Cat" (19) " " (20) " C" (21) " Ca" (22) " Cat" (23) "C" (24) "Ca" (25) "Cat" (26) "a" (27) "at" (28) "t" (29) "" , "" is a substring of every string

Note: Totalnumber of substrings of a string of length N is (N * (N + 1)) / 2. This is after excluding the empty string "" because it is a substring of all strings.

Approach:

Let us consider a string which has n characters:

For each character at index i (0 to n-1): find substrings of length 1, 2, ..., n-i

Example: Let our string be cat, here n = 3 (the length of string) here, index of 'c' is 0 index of 'a' is 1 index of 't' is 2

Loop from i = 0 to 2: (since n-1 = 2)

When i = 0: Substring of length 1 : "c"
Substring of length 2 : "ca" Substring of length 3 : "cat" , (substring of length n-i or 3-0 = 3)

When i = 1: Substring of length 1 : "a" Substring of length 2 : "at" , (substring of length n-i or 3-1 = 2)

When i = 2: Substring of length 1 : "t" , (substring of length n-i or 3-2 = 1)

Example:

Java `

// Java Program to split a string into all possible // substrings excluding the string with 0 characters i.e. ""

import java.io.*; import java.util.ArrayList;

class SubstringsOfAString {

// function to split a string into all its substrings
// and return the list as an object of ArrayList
public static ArrayList<String>
splitSubstrings(String s)
{

    // variables to traverse through the
    // string
    int i, j;

    // to store the length of the
    // string
    int stringLength = s.length();

    // List object to store the list of
    // all substrings of the string s
    ArrayList<String> subStringList
        = new ArrayList<String>();

    // first for loop
    for (i = 0; i < stringLength; i++) {

        for (j = i + 1; j <= stringLength; j++) {

            subStringList.add(s.substring(i, j));
        }

    } // end of first for loop

    // returning the list (object
    // of ArrayList) of substrings
    // of string s
    return subStringList;
}

public static void main(String[] args)
{

    // here "The Cat" is our input string
    String stringInput = new String("The Cat");

    ArrayList<String> subStringList
        = SubstringsOfAString.splitSubstrings(
            stringInput);

    System.out.println(
        "\nSubstring list printed as an ArrayList : ");
    System.out.println(subStringList);

    System.out.println(
        "\n\nAll substrings printed 1 per line : ");
    int count = 1;

    // each substring would be printed
    // within double quotes
    for (String it : subStringList) {
        System.out.println("(" + count + ") \"" + it
                           + "\"");
        count++;
    }
}

}

Output

Substring list printed as an ArrayList : [T, Th, The, The , The C, The Ca, The Cat, h, he, he , he C, he Ca, he Cat, e, e , e C, e Ca, e Cat, , C, Ca, Cat, C, Ca, Cat, a, at, t]

All substrings printed 1 per line : (1) "T" (2) "Th" (3) "The" (4) "The " (5) "The C" (6) "The Ca" (7) "The Cat" (8) "h" (9) "he" (10) "he " (11) "he C" (12) "he Ca" (13) "he Cat" (14) "e" (15) "e " (16) "e C" (17) "e Ca" (18) "e Cat" (19) " " (20) " C" (21) " Ca" (22) " Cat" (23) "C" (24) "Ca" (25) "Cat" (26) "a" (27) "at" (28) "t"

Time Complexity: O(n2) where n is the length of a string

Output 1: When string Input = bat

Substring list printed as an ArrayList : [b, ba, bat, a, at, t]

All substrings printed 1 per line : (1) "b" (2) "ba" (3) "bat" (4) "a" (5) "at" (6) "t"

Output 2: When string Input = The Cat

Substring list printed as an ArrayList : [T, Th, The, The , The C, The Ca, The Cat, h, he, he , he C, he Ca, he Cat, e, e , e C, e Ca, e Cat, , C, Ca, Cat, C, Ca, Cat, a, at, t]