438. 找到字符串中所有字母异位词（Java、滑动窗口）

标准滑动窗口框架
把每次收缩的窗口长度符合的保存到集合中即可

lass Solution {
    public List<Integer> findAnagrams(String s, String p) {
        Map<Character,Integer> need = new HashMap<>();
        List<Integer> res = new ArrayList<>();
        int right = 0,left = 0;
        int valid = 0;
        int sizeS = s.length();
        int sizeP = p.length();
        if(sizeP>sizeS){
            return res;
        }
        for(char c :p.toCharArray()){
            need.put(c,need.getOrDefault(c,0)+1);
        }

        int needSize = need.size();

        Map<Character,Integer> window = new HashMap<>();
        while(right < sizeS){
            char c = s.charAt(right);
            right++;
            if(need.containsKey(c)){
                window.put(c,window.getOrDefault(c,0)+1);
                if(window.get(c).equals(need.get(c))){
                    valid++;
                }
            }
            
            while(valid==needSize){
                if(right-left==sizeP){
                    res.add(left);
                }
                c = s.charAt(left);
                left++;
                if(need.containsKey(c)){
                    if(window.get(c).equals(need.get(c))){
                        valid--;
                    }
                    window.put(c,window.get(c)-1);
                }
            }
        }
        return res;
    }
}