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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"].

比较经典的题目
思路:用hashmap扫一遍,出现过的就加到list上去,为了不使结果重复,当碰到重复的时候更新value。
public class Solution {    public List<String> findRepeatedDnaSequences(String s) {        List<String> res=new ArrayList<>();        if(s==null)return res;        Map<String,Integer> check=new HashMap<>();        for(int i=0;i<=s.length()-10;i++){            String sub=s.substring(i,i+10);            if(!check.containsKey(sub)){                check.put(sub,1);            }else{                if(check.get(sub)==1){                    res.add(sub);                    check.put(sub,2);                }            }        }        return res;    }}

 

187. Repeated DNA Sequences