438. Find All Anagrams in a String

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

1. Use STL sort():

//TLE
class Solution {
public:
    vector<int> findAnagrams(string s, string p) {
        vector<int> result;
        if(p.length()>s.length())
            return result;
        string sub = "";
        int n = p.length();
        int i;
        int sum = 0;
        for(i = 0; i <= s.length() - n; i++){
            sub = s.substr(i, n);
            if(isAnagram(sub, p)){
                result.push_back(i);
                break;
            }
        }
        return result;
    }
private:
    bool isAnagram(string sub, string p){
        sort(sub.begin(), sub.end());
        sort(p.begin(), p.end());
        return sub==p;
    }
};
//1. check is that possible s contains p 
//2. pick up count of letters in p
//3. in s, pick substring with p.size() and consider is it an anagram of p
//4. return the index if step 3 is true
//5. return result

2. Use sliding the window:

//32 ms    8.5 MB
class Solution {
public:
    vector<int> findAnagrams(string s, string p) {
        vector<int> result;
        if(p.length()>s.length())
            return result;
        vector<int> s_vec(26,0), p_vec(26,0);
        int i;
        for(i = 0; i < p.length(); i++){
            p_vec[p[i]-'a']++; //add count of letter p[i]
            s_vec[s[i]-'a']++; //add count of letter s[i]
        }
        if(p_vec==s_vec)
            result.push_back(0);
        for(; i < s.length(); i++){ //until the window reaches the end
            s_vec[s[i]-'a']++; //add count of letter s[i]
            s_vec[s[i-p.size()]-'a']--; //remove count of the previous head
            if(p_vec==s_vec)
                result.push_back(i-p.size()+1);
        }
        return result;
    }
};