LeetCode 187. 重复的DNA序列

原题链接：https://leetcode.cn/problems/repeated-dna-sequences/?envType=daily-question&envId=2023-11-05

用字符串哈希处理，可以在O(1)时间内查出前面是否有长度为10的相同串

时间复杂度为O(n) 空间复杂度O(n)

C++代码

class Solution {
public:
    typedef unsigned long long ull;
    const int P = 131;
    ull h[100000+5],p[100000+5];
    ull get(int l,int r){
        return h[r] - h[l-1]*p[r-l+1];
    }
    vector findRepeatedDnaSequences(string s) {
        vectorres;
        unordered_mapmp;
        p[0] = 1; // p^0 = 1
        h[0] = 0;
        s = " "+s;
        int n = s.length();
        for(int i=1;i<=n;i++){
            p[i] = p[i-1]*P;
            h[i] = h[i-1]*P + s[i];
        }
        int l = 1,r = 10;
        while(r<=n){
            ull key = get(l,r);
            if(mp[key]==1) res.push_back(s.substr(l,10));
            mp[key]++;
            l++,r++;
        }
        return res;
    }       
};