使用滑动窗口算法求解：

class Solution {
public:
    vector<int> findAnagrams(string s, string p) {
        vector<int> res;
        unordered_map<char,int> need,window;
        int left = 0,right = 0,match_cnt = 0;
        //更新需要命中的全部字符
        for(auto c:p) need[c] += 1;
        
        while(right < s.size()){
            char c = s[right];
            right++;
            if(need.count(c))
            {
                window[c] +=1 ;
                if(window[c] == need[c])
                    match_cnt += 1;
            }
            
            while(right - left >= p.size())
            {
                if(match_cnt == need.size())
                    res.push_back(left);
                char c = s[left];
                left += 1;
                if(need.count(c))
                {
                    if(need[c] == window[c])
                        match_cnt -= 1;
                    window[c] -= 1;
                }
            }
        }
        
        return res;
    }
};

运行效率:

Runtime: 20 ms, faster than 48.14% of C++ online submissions for Find All Anagrams in a String.
Memory Usage: 8.6 MB, less than 57.35% of C++ online submissions for Find All Anagrams in a String.