LeetCode-187 Repeated DNA Sequences

题目描述

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.

题目大意

给定一个字符串，寻找字符串中长度为10的并且出现不止一次的子串。

示例

E1

Input: s = "AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT"

Output: ["AAAAACCCCC", "CCCCCAAAAA"]

解题思路

利用unordered_map保存不同子串出现的次数，最后遍历map查找符合条件的子串。

复杂度分析

时间复杂度：O(n)

空间复杂度：O(n)

代码

class Solution {
public:
    vector<string> findRepeatedDnaSequences(string s) {
        vector<string> res;
        if(s.length() < 10)
            return res;
        
        unordered_map<string, int> m;
        string subs = s.substr(0, 10);
        m[subs]++;
        //记录不同子串出现的次数
        for(int i = 10; i < s.length(); i++) {
            subs.erase(0, 1);
            subs += s[i];
            m[subs]++;
        }
        
        unordered_map<string, int>::iterator iter = m.begin();
        //遍历寻找出现多次的子串
        for(; iter != m.end(); iter++) {
            if(iter->second > 1)
                res.push_back(iter->first);
        }
        
        return res;
    }
};