438. Find All Anagrams in a String

滑动窗口法:

public static List<Integer> findAnagrams(String s, String p) {
    List<Integer> res = new ArrayList<>();
    if (s.length() == 0 || p.length() == 0 || s.length() < p.length()) {
      return res;
    }
    int[] chars = new int[26];
    for (int i = 0; i < p.length(); i++) {
      chars[p.charAt(i) - 'a']++;
    }
    int start = 0, end = 0, len = p.length(), diff = len;
    while (end<len){
      chars[s.charAt(end)-'a']--;
      if(chars[s.charAt(end)-'a']>=0){
        diff--;
      }
      end++;
    }
    if(diff==0) res.add(0);
    while(end<s.length()){
      if(chars[s.charAt(start)-'a']>=0){
        diff++;
      }
      chars[s.charAt(start)-'a']++;
      start++;

      chars[s.charAt(end)-'a']--;
      if(chars[s.charAt(end)-'a']>=0){
        diff--;
      }
      if(diff==0)
        res.add(start);
      end++;
    }

    return res;
  }