KMP ALGO.java

class Solution {
    public List<String> stringMatching(String[] words) {
        List<String> result = new ArrayList<>();
        int n = words.length;
        
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                if (i != j && kmpSearch(words[j], words[i])) {
                    result.add(words[i]);
                    break; // No need to check further for this word
                }
            }
        }
        return result;
    }

    // KMP Algorithm
    private boolean kmpSearch(String text, String pattern) {
        int[] lps = computeLPSArray(pattern);
        int i = 0; // Pointer for text
        int j = 0; // Pointer for pattern

        while (i < text.length()) {
            if (text.charAt(i) == pattern.charAt(j)) {
                i++;
                j++;
            }

            if (j == pattern.length()) {
                return true; // Pattern found
            } else if (i < text.length() && text.charAt(i) != pattern.charAt(j)) {
                if (j != 0) {
                    j = lps[j - 1];
                } else {
                    i++;
                }
            }
        }
        return false; // Pattern not found
    }

    // Compute Longest Prefix Suffix (LPS) array for KMP
    private int[] computeLPSArray(String pattern) {
        int m = pattern.length();
        int[] lps = new int[m];
        int len = 0;
        int i = 1;

        while (i < m) {
            if (pattern.charAt(i) == pattern.charAt(len)) {
                len++;
                lps[i] = len;
                i++;
            } else {
                if (len != 0) {
                    len = lps[len - 1];
                } else {
                    lps[i] = 0;
                    i++;
                }
            }
        }
        return lps;
    }
}