[LC] 438. Find All Anagrams in a String

Given a string s and a non-empty string p, find all the start indices of p's anagrams in s.

Strings consists of lowercase English letters only and the length of both strings s and p will not be larger than 20,100.

The order of output does not matter.

Example 1:

Input:
s: "cbaebabacd" p: "abc"

Output:
[0, 6]

Explanation:
The substring with start index = 0 is "cba", which is an anagram of "abc".
The substring with start index = 6 is "bac", which is an anagram of "abc".

Example 2:

Input:
s: "abab" p: "ab"

Output:
[0, 1, 2]

Explanation:
The substring with start index = 0 is "ab", which is an anagram of "ab".
The substring with start index = 1 is "ba", which is an anagram of "ab".
The substring with start index = 2 is "ab", which is an anagram of "ab".

Time: O(N)

class Solution:
    def findAnagrams(self, s: str, p: str) -> List[int]:

        my_dict = {}
        res = []
        count = 0
        for char in p:
            freq = my_dict.get(char, 0)
            my_dict[char] = freq + 1

        for i in range(len(s)):
            char = s[i]
            if char in my_dict:
                my_dict[char] -= 1
                if my_dict[char] == 0:
                    count += 1

            if i >= len(p):
                start = i - len(p)
                start_char = s[start]
                if start_char in my_dict:
                    my_dict[start_char] += 1
                    if my_dict[start_char] == 1:
                        count -= 1
            # check my_dict size instead of len(p)
            if count == len(my_dict):
                res.append(i - len(p) + 1)
        return res

public class Solution {
  public List<Integer> allAnagrams(String sh, String lo) {
    // Write your solution here
    Map<Character, Integer> map = new HashMap<>();
    char[] charArr = sh.toCharArray();
    for (int i = 0; i < charArr.length; i++) {
      map.put(charArr[i], map.getOrDefault(charArr[i], 0) + 1);
    }

    List<Integer> res = new ArrayList<>();
    char[] lCharArr = lo.toCharArray();
    int count = 0;
    int start = 0;
    for (int i = 0; i < lCharArr.length; i++) {
      char cur = lCharArr[i];
      if (map.containsKey(cur)) {
        int num = map.get(cur);
        if (num == 1) {
          count += 1;
        }
        map.put(cur, num - 1);
      }

      if (i >= sh.length()) {
        start = i - sh.length();
        if (map.containsKey(lCharArr[start])) {
          int startNum = map.get(lCharArr[start]);
          if (startNum == 0) {
            count -= 1;
          }
          map.put(lCharArr[start], startNum + 1);
        }
      }

      if (count == map.size()) {
        res.add(i - sh.length() + 1);
      }
    }
    return res;
  }
}