187 Repeated DNA Sequences

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本文介绍了一种算法，用于从DNA分子中找出所有长度为10个字母且出现次数超过一次的重复序列。通过使用哈希映射的方式进行优化，使得算法能够高效地处理大规模的数据。

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1 题目

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.

Example:

Input: s = "AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT"

Output: ["AAAAACCCCC", "CCCCCAAAAA"]

2 尝试解

class Solution {
public:
    vector<string> findRepeatedDnaSequences(string s) {
        vector<string> result;
        map<string,int> saver;
        if(s.size() < 10) return result;
        for(int i = 0; i < s.size()-9;i++){
            string temp = s.substr(i,10);
            if(saver.count(temp)!=0 && saver[temp]==0){
                result.push_back(temp);                
                saver[temp] = 1;
            }
            else if(saver.count(temp)==0){
                saver[temp] = 0;
            }
        }
        return result;
    }
};

3 标准解

class Solution {
public:
    vector<string> findRepeatedDnaSequences(const string &s) {
        vector<string> result;
        unordered_map<int, int> count;
        for (int i = 0, h = 0; i < s.size(); i++) {
            h = ((h & 0x07ffffff) << 3) | (s[i] & 7);
            if ((count[h]++) == 1) {
                result.push_back(s.substr(i - 9, 10));
            }
        }
        return result;
    }
};