438. Find All Anagrams in a String**

​​https://leetcode.com/problems/find-all-anagrams-in-a-string/​​

題目描述

Given a string ​

​s​

​​ and a non-empty string ​

​p​

​​, find all the start indices of ​

​p​

​​'s anagrams in ​

​s​

​.

Strings consists of lowercase English letters only and the length of both strings ​

​s​

​​ and ​

​p​

​​ will not be larger than ​

​20100​

​.

The order of output does not matter.

Example 1:

Input:
s: "cbaebabacd" p: "abc"

Output:
[0, 6]

Explanation:
The substring with start index = 0 is "cba", which is an anagram of "abc".
The substring with start index = 6 is "bac", which is an anagram of "abc".      

Input:
s: "abab" p: "ab"

Output:
[0, 1, 2]

Explanation:
The substring with start index = 0 is "ab", which is an anagram of "ab".
The substring with start index = 1 is "ba", which is an anagram of "ab".
The substring with start index = 2 is "ab", which is an anagram of "ab".      

C++ 實作 1

class Solution {
public:
    vector<int> findAnagrams(string s, string p) {
        vector<int> res, pv(256, 0), sv(256, 0);
        if (s.empty() || p.empty() || (s.size() < p.size()))
            return res;
        
        for (int i = 0; i < p.size(); ++i) {
            ++pv[p[i]];
            ++sv[s[i]];
        }
        if (sv == pv) res.push_back(0);
        for (int i = p.size(); i < s.size(); ++i) {
            ++sv[s[i]];
            --sv[s[i - p.size()]];
            // 注意最後傳回的是字元串開始的索引.
            if (pv == sv) res.push_back(i - p.size() + 1);
        }
        return res;
    }
};