LeetCode 187 Repeated DNA Sequences (Map)

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"].

题目链接：https://leetcode.com/problems/repeated-dna-sequences/

题目分析：用map记录长度为10的子串出现的次数，不知道为什么leet上不支持hashtable，只能用hashmap，注意hashmap的不能为空，字符串用StringBuffer非常方便

public class Solution {
    public List findRepeatedDnaSequences(String s) {
        int len = s.length();
        List ans = new ArrayList<>();
        if(len < 10) {
            return ans;
        }
        Map mp = new HashMap<>();
        StringBuffer cur = new StringBuffer(s.substring(0, 10));
        String t = cur.toString();
        mp.put(t, 1);
        for(int i = 10; i < len; i++) {
            cur.append(s.charAt(i));
            cur.deleteCharAt(0);
            t = cur.toString();
            if(mp.containsKey(t)) {
                mp.put(t, mp.get(t) + 1);
                if((int)mp.get(t) == 2) {
                    ans.add(t);
                }
            }
            else {
                mp.put(t, 1);
            }
        }
        return ans;
    }
}