leetcode 187. Repeated DNA Sequences_leetcode 187 csdn cpp-优快云博客

本文介绍了一种高效的方法来找出DNA分子中长度为10个字符且出现多次的序列。通过使用两个Set数据结构，该方法能够快速识别出所有符合条件的重复序列。

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All DNA is composed of a series of nucleotides abbreviated as A, C, G, and T, for example: "ACGAATTCCG". When studying DNA, it is sometimes useful to identify repeated sequences within the DNA.

Write a function to find all the 10-letter-long sequences (substrings) that occur more than once in a DNA molecule.

For example,

Given s = "AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT",

Return:
["AAAAACCCCC", "CCCCCAAAAA"].

使用indexOf方法查找string位置的方法果断超时了

非常简短的方法，用到两个Set

public List<String> findRepeatedDnaSequences(String s) {
    Set seen = new HashSet(), repeated = new HashSet();
    for (int i = 0; i + 9 < s.length(); i++) {
        String ten = s.substring(i, i + 10);
        if (!seen.add(ten))
            repeated.add(ten);
    }
    return new ArrayList(repeated);
}

还有巧妙地用到条件使用位操作

public List<String> findRepeatedDnaSequences(String s) {
    Set<Integer> words = new HashSet<>();
    Set<Integer> doubleWords = new HashSet<>();
    List<String> rv = 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 < s.length() - 9; i++) {
        int v = 0;
        for(int j = i; j < i + 10; j++) {
            v <<= 2;
            v |= map[s.charAt(j) - 'A'];
        }
        if(!words.add(v) && doubleWords.add(v)) {
            rv.add(s.substring(i, i + 10));
        }
    }
    return rv;
}