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"].
参考：http://blog.csdn.net/coderhuhy/article/details/43647731

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;


public class Solution {
    public List<String> findRepeatedDnaSequences(String s) {
        if(s.length() < 10)
            return new ArrayList<String>();
        List<String> result = new ArrayList<String>();                                    //结果集
        Map<Character, Integer> dict = new HashMap<Character, Integer>();                //ACGT对应的整数编码
        Map<Integer, Integer> check = new HashMap<Integer, Integer>();                    //存放已经放到结果集中字符串，用于去重
        Map<Integer, Integer> subValue = new HashMap<Integer, Integer>();                //遍历过的子串，用于检查重复子串 
        int erase = 0x0003ffff;
        
        dict.put('A', 0);
        dict.put('C', 1);
        dict.put('G', 2);
        dict.put('T', 3);
        
        int hint = 0;
        
        for(int i = 0; i < 10; i++){
            hint <<= 2;
            hint += dict.get(s.charAt(i));
        }
        
        subValue.put(hint, 1);
        //
        for(int i = 10; i < s.length(); i++){
            hint = ((hint & erase) << 2) + dict.get(s.charAt(i));
            if(subValue.get(hint) != null){                            //遇到重复的子串
                if(check.get(hint) == null){                        //结果集中没有,放到结果集和check中
                    result.add(s.substring(i - 9, i + 1));
                    check.put(hint, 1);
                }//if
            }//if
            subValue.put(hint, 1);
        }
        
        return result;
    }
}