Repeated DNA Sequences

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 *
 * @author zhiyong wang
 * title: Repeated DNA Sequences
 * content:
 *  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"].
 *
 */
public class RepeatedDNASequences {

//自己很不细心，错了好几个地方（1）自己没有把思路想好，就开始动笔写代码
    //（2）上来第一步没有考虑特殊情况
    //(3)每次取值范围是（i,i+10）,这两个值都没有注意，直接写的（0,10）
    //(4)只考虑了set是否包含，没有考虑set的写入情况
    //（5）没有考虑如果存在多个重复，是否要多次插入情况
    public List<String> findRepeatedDNASequences(String s){
        int length = s.length();
        List list = new ArrayList();
        if(s == null || length < 10) return list;
        Set set = new HashSet();
        for(int i=0;i<length-9;i++){
            String temp = s.substring(i, i+10);
            if(set.contains(temp) && !list.contains(temp)){
                list.add(temp);
            }else{
                set.add(temp);
            }
            
        }
        return list;
    }
    public static void main(String[] args) {
        RepeatedDNASequences r = new RepeatedDNASequences();
        r.findRepeatedDNASequences("CAAAAAAAAAC");
    }
}