代码1

Runtime: 43 ms, faster than 11.05% of Java online submissions for Repeated DNA Sequences.

class Solution {
    public List<String> findRepeatedDnaSequences(String s) {
        Set<Integer> first = new HashSet();
        Set<Integer> second = new HashSet();
        List<String> ans = new ArrayList();
        char[] map = new char[26];
        map['A' - 'A'] = 0;
        map['C' - 'A'] = 1;
        map['G' - 'A'] = 2;
        map['T' - 'A'] = 3;
        for (int i = 0; i + 9 < s.length(); i++) {
            String sub = s.substring(i, i + 10);
            int sequence = 0;
            for (int j = 0; j < 10; j++) {
                sequence = sequence << 2;
                sequence = sequence | map[sub.charAt(j) - 'A'];
            }
            if (!first.add(sequence) && second.add(sequence)) ans.add(sub);
        }
        return ans;
    }
}