leetcode187. Repeated DNA Sequences

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本文介绍了一种使用两个哈希集合来查找DNA分子中长度为10且出现多次的子序列的方法。通过遍历输入字符串并检查每个可能的10字母长的子串是否已存在，该方法能有效地找出所有重复序列。

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187. Repeated DNA Sequences

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"].

解法

维护两个hashset。

public class Solution {
    public List<String> findRepeatedDnaSequences(String s) {
        List<String> ret = new ArrayList<>();
        if (s == null || s.length() < 10) {
            return ret;
        }

        Set<String> set = new HashSet<String>();
        Set<String> repet = new HashSet<String>();
        for (int i = 0; i < s.length() - 9; i++) {
            String sub = s.substring(i, i + 10);
            if (!set.add(sub)) {
                repet.add(sub);
            }
        }

        return new ArrayList<>(repet);
    }
}