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"].

思路：
使用hashmap来处理，要注意避免添加已经添加过的元素。

class Solution {
    public List<String> findRepeatedDnaSequences(String s) {
        List<String> res = new LinkedList<>();
        HashMap<String,Integer> maps = new HashMap<>();

        int length = s.length();
        if(length <= 10)
            return res;

        for(int i = 0;i <= length-10;i++){
            String subStr = s.substring(i,i+10);
            if(maps.containsKey(subStr)){
                if(maps.get(subStr) == 1){
                    maps.replace(subStr,-1);
                    res.add(subStr);
                }
            }else{
                maps.put(subStr,1);
            }
        }
        return res;
    }
}