Leetcode187: 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"].

题意：

给出一串字符串，找出其中长度为10的出现次数大于1的子串。

解法：

可以先将s的所有长度为10的子串（共s.size()-9个）存在vector dict中，然后对dict进行sort，遍历sort后的dict，找出出现次数大于1次的string，返回这些string即可。

复杂度：

dict的规模是n-9，所以sort dict为O(nlogn)，遍历O(n)。时间复杂度为O(nlogn)。
空间复杂度O(n)。

代码：

class Solution {public:    vector<string> findRepeatedDnaSequences(string s) {        vector<string> dict;        vector<string> res;        int sLen=s.size();        if(sLen<=10) return res;        for(int i=0; i<=sLen-10; i++){            string str=s.substr(i, 10);            dict.push_back(str);        }        sort(dict.begin(), dict.end());        int dLen=dict.size();        int count=1;        for(int i=1; i<dLen; i++){            if(dict[i]==dict[i-1])            count++;            else{                if(count>1){                    res.push_back(dict[i-1]);                    count=1;                }            }        }        if(dict[dLen-1]==dict[dLen-2])        res.push_back(dict[dLen-1]);        return res;    }};