Sliding.java

import java.util.*;
import java.util.Map;
class Sliding {
    public List<Integer> findSubstring(String s, String[] words) {
        List<Integer> result = new ArrayList<>();

        if (s == null || words.length == 0) return result;

        int wordLen = words[0].length();
        int wordCount = words.length;
        int totalLen = wordLen * wordCount;

        Map<String, Integer> wordMap = new HashMap<>();
        for (String word : words) {
            wordMap.put(word, wordMap.getOrDefault(word, 0) + 1);
        }

        for (int i = 0; i < wordLen; i++) {
            int left = i, count = 0;
            Map<String, Integer> windowMap = new HashMap<>();

            for (int j = i; j + wordLen <= s.length(); j += wordLen) {
                String word = s.substring(j, j + wordLen);

                if (wordMap.containsKey(word)) {
                    windowMap.put(word, windowMap.getOrDefault(word, 0) + 1);
                    count++;

                    while (windowMap.get(word) > wordMap.get(word)) {
                        String leftWord = s.substring(left, left + wordLen);
                        windowMap.put(leftWord, windowMap.get(leftWord) - 1);
                        left += wordLen;
                        count--;
                    }

                    
                    if (count == wordCount) {
                        result.add(left);

                        String leftWord = s.substring(left, left + wordLen);
                        windowMap.put(leftWord, windowMap.get(leftWord) - 1);
                        left += wordLen;
                        count--;
                    }
                } else {
            
                    windowMap.clear();
                    count = 0;
                    left = j + wordLen;
                }
            }
        }

        return result;
    }

    public static void main(String[] args){
    String s = "barfoothefoobarman";
    String[] words = {"foo", "bar"};

    Sliding obj = new Sliding(); 
    List<Integer> ans = obj.findSubstring(s, words); // correct call

    System.out.println(ans);
}
}