Java: Find all the start indices of a given string's anagrams in another specified string

Last update on May 13 2025 13:00:24 (UTC/GMT +8 hours)

Find Anagram Start Indices

Write a Java program to find all the start indices of a given string's anagrams in another given string.

Visual Presentation:

Sample Solution:

Java Code:

// Importing necessary Java utilities
import java.util.*;
// Main class
public class Main {
    // Main method
    public static void main(String[] args) {
        // Declaring and initializing two strings
        String str1 = "zyxwyxyxzwxyz";
        String str2 = "xyz";
        // Printing the original strings
        System.out.println("Original String: " + str1);
        System.out.println("Starting anagram indices of " + str2 + ": " + find_Anagrams(str1, str2));
    }
    // Method to find the starting indices of anagrams of str2 in str1
    public static List<Integer> find_Anagrams(String str1, String str2) {
        // Creating a list to store starting indices of anagrams
        List<Integer> list = new ArrayList<>();
        // Check if str1 is smaller than str2 or str2 is empty
        if (str1.length() < str2.length() || str2.length() < 1) {
            return list;
        }
        // If str1 is the same as str2, add 0 as the starting index
        if (str1.equals(str2)) {
            list.add(0);
            return list;
        }
        // Creating a HashMap to store character frequencies in str2
        HashMap<Character, Integer> map = new HashMap<>();
        for (char c : str2.toCharArray()) {
            if (map.containsKey(c)) {
                map.put(c, map.get(c) + 1);
            } else {
                map.put(c, 1);
            }
        }
        // Variables to track lengths and count of correct characters
        int str2_length = str2.length();
        int current_length = 0;
        int correct_chars = 0;
        // Looping through str1 to find anagrams of str2
        for (int i = 0; i < str1.length(); ++i) {
            current_length++;
            if (map.containsKey(str1.charAt(i))) {
                int ctr = map.get(str1.charAt(i));
                if (ctr > 0) {
                    correct_chars++;
                }
                map.put(str1.charAt(i), ctr - 1);
            }
            if (current_length == str2_length) {
                int begin_pos = i - str2_length + 1;
                if (correct_chars == str2_length) {
                    list.add(begin_pos);
                }
                if (map.containsKey(str1.charAt(begin_pos))) {
                    int ctr = map.get(str1.charAt(begin_pos));
                    if (ctr >= 0) {
                        correct_chars--;
                    }
                    map.put(str1.charAt(begin_pos), ctr + 1);
                }
                current_length--;
            }
        }
        return list;
    }
}

Sample Output:

Original String: zyxwyxyxzwxyz
Starting anagram indices of xyz: [0, 6, 10]

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to find all starting indices of palindromic substrings in a given string.
• Write a Java program to locate all starting indices where any permutation of a given pattern appears in a string.
• Write a Java program to identify the longest substring of a string that is an anagram of a given word.
• Write a Java program to count the total occurrences of anagrammatic substrings of a given pattern within a string.

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Company:  Amazon

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