最长重复子串

/*
 * Leetcode Problem 1062: Longest Repeating Substring
 * 
 * Problem Statement:
 * Given a string s, find out the length of the longest repeating substring(s). The repeating substring should not overlap.
 * 
 * Approach:
 * 1. Use binary search to find the maximum length of the repeating substring.
 * 2. Use a hash set to store the substrings of a given length and check for repeats.
 * 3. If a repeating substring is found, increase the search length; otherwise, decrease it.
 * 
 * Using Java Streams for substring extraction and checking repeats.
 */

import java.util.HashSet;
import java.util.stream.IntStream;

public class LongestRepeatingSubstringStream {
    public int longestRepeatingSubstring(String s) {
        int n = s.length();
        int left = 1, right = n;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (hasRepeatingSubstring(s, mid)) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }
        return left - 1;
    }

    private boolean hasRepeatingSubstring(String s, int length) {
        HashSet<String> seen = new HashSet<>();
        return IntStream.range(0, s.length() - length + 1)
                .mapToObj(i -> s.substring(i, i + length))
                .anyMatch(substring -> !seen.add(substring));
    }
}