week 2 438. Find All Anagrams in a String

public class Solution {
    public List<Integer> findAnagrams(String s, String p) {
        List<Integer> res = new ArrayList<>();
        if(s == null || s.length() == 0 || p = null || p.length() == 0){
            return res;
        }
        
        int [] map = new int [256];
        for (char cur: p.toCharArray()){
            map[cur]++;
        }
    int left = 0;
    int right = 0;
    int counter = p.length();
        
    while(right < s.length()){
        if(map[s.charAt(right)]) > 0{
            counter--;
        }
        
        map[s.charAr(right)]--;
        right++;
        
        if (counter == 0){
            res.add(left);
        }
        
        if(right - left == p.length()){
            if(map[s.charAt(left)] >= 0){
                counter++;
            }
            map[s.charAt(left)]++;
            left++;
        }
    }
        return res;
    }
    
}