Leetcode 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"].

基本思路就是利用hash的方法求出对用10 character的value

每一个字母分配一个对应的初始值

public class Solution {    public List<String> findRepeatedDnaSequences(String s) {        Set<Integer> firstTime = new HashSet<>();        Set<Integer> secondTime = new HashSet<>();        List<String> results = new ArrayList<>();        int[] word = new int[26];        word['A' - 'A'] = 0;        word['C' - 'A'] = 1;        word['G' - 'A'] = 2;        word['T' - 'A'] = 3;                     for(int i = 0; i < s.length() - 9; i++){            int value = 0;            for(int j = 0; j < i + 10; j++){                value <<=2;                value |= word[s.charAt(j) - 'A'];//注意这一步hashing            }            if(!firstTime.contains(value)){                firstTime.add(value);            }else if(!secondTime.contains(value)){                secondTime.add(value);                results.add(s.substring(i, i + 10));            }        }        return results;    }}