187. 重复的DNA序列

public List<String> findRepeatedDnaSequences(String s) {
        List<String> res = new ArrayList<>();
        Set<String> resSet = new HashSet<>();
        if (s.length() < 10) return res;
        Set<String> set = new HashSet<>();

        for (int lo = 0, hi = lo + 10; hi <= s.length(); lo++,hi++) {
            String sub = s.substring(lo, hi);

            if (!set.add(sub)) {
                resSet.add(sub);
            }
        }
        res.addAll(resSet); 
        return res;
    }


Rabin-Karp算法
public List<String> findRepeatedDnaSequences(String s) {
        int M = 10;
        int R = 4;
        int RM = (int)Math.pow(4, 10);
        
        int n = s.length();
        if (n <= M) return new ArrayList<String>();
        
        Map<Character, Integer> map = new HashMap<Character, Integer>(){{put('A', 0); put('C', 1); put('G', 2); put('T', 3);}};
        int[] nums = new int[n];
        
        for (int i = 0; i < n; i++) {
            nums[i] = map.get(s.charAt(i));
        }
        
        int h = 0;

        Set<Integer> seen = new HashSet<>();
        Set<String>  res  = new HashSet<>();
        
        for (int i = 0; i < n-M+1; i++) {
            if (i != 0) {
                h = h * R - nums[i-1] * RM + nums[i+M-1];
            } 
            else {
                for (int j = 0; j < n; j++) {
                    h = h * R + nums[i];
                }
            }
            
            if (seen.contains(h)) {
                res.add(s.substring(i, i + M));
            }
            
            seen.add(h);
        }
        
        return new ArrayList<String>(res);
    }