FindAllAnagramsInAString.java

// https://leetcode.com/problems/find-all-anagrams-in-a-string/
// #hash-table
class Solution {
  public List<Integer> findAnagrams(String s, String p) {
    // count frequency of all characters inside p
    // for each left => end at current ith => check it whether is an anagram with counting frequency
    // ..

    int[] frequencyAnagram = new int['z' - 'a' + 1];
    int[] currentFrequency = new int['z' - 'a' + 1];
    for (char c : p.toCharArray()) {
      frequencyAnagram[c - 'a'] += 1;
    }

    int left = 0;
    int len = p.length();
    ArrayList<Integer> result = new ArrayList();
    for (int i = 0; i < s.length(); i++) {
      currentFrequency[s.charAt(i) - 'a'] += 1;
      if (i - left + 1 == len) {
        if (Arrays.equals(frequencyAnagram, currentFrequency)) {
          result.add(left);
        }
        currentFrequency[s.charAt(left) - 'a'] -= 1;
        left += 1;
      }
    }
    return result;
  }
}