[Leetcode] 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"].

大神的代码： http://blog.csdn.net/wzy_1988/article/details/44224749

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Native method:

 public class Solution {
     public List<String> findRepeatedDnaSequences(String s) {
         List<String> res = new ArrayList<>();
         if(s == null || s.length() < 2)
             return res;
         HashMap<String, Integer> hm = new HashMap<>();
         for(int i = 0; i < s.length() - 9; ++i) {
             String temp = s.substring(i, i + 10);
             if(hm.containsKey(temp))
                 hm.put(temp, hm.get(temp) + 1);
             else
                 hm.put(temp, 1);
         }
         for(Map.Entry<String, Integer> entry: hm.entrySet()) {
             if(entry.getValue() > 1)
                 res.add(entry.getKey());
         }
         return res;
     }
 }

但是这种写法浪费了太多的空间。

－－－－－－－－－－－－－－－－－－－－－－－－－－－

Method 2: 利用二进制， 存储整数。

http://segmentfault.com/a/1190000002601702