Day_31.java

// Group Anagrams
class Solution {
    public List<List<String>> groupAnagrams(String[] strs) {
        List<List<String>> ans = new ArrayList<>();
        int n = strs.length;
        if(n == 0) return ans;
        HashMap<String,List<String>> mpp = new HashMap<>();
        for(int i=0;i<n;i++){
            char[] arr = strs[i].toCharArray();
            Arrays.sort(arr);
            String s = new String(arr);
            if(mpp.containsKey(s)){
                mpp.get(s).add(strs[i]);
            }
            else{
                mpp.put(s,new ArrayList<>(Arrays.asList(strs[i])));
            }
        }
        for(var it : mpp.values()){
            ans.add(it);
        }
        return ans;       
    }
}



//  Longest Substring Without Repeating Characters
class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length();
        int[] hash = new int[256];
        Arrays.fill(hash,-1);
        int maxlen = 0, l = 0;
        for(int r=0;r<n;r++){
            char ch = s.charAt(r);
            if(hash[ch] >= l) l = hash[ch] + 1;
            hash[ch] = r;
            maxlen = Math.max(maxlen,r-l+1);
        }
        return maxlen;
    }
}



// Maximum Length Substring With Two Occurrences
class Solution {
    public int maximumLengthSubstring(String s) {
        int n = s.length();
        int maxlen = 0, l = 0;
        int[] hash = new int[26];
        for(int r=0;r<n;r++){
            char ch = s.charAt(r);
            hash[ch-'a']++;
            while(hash[ch-'a'] > 2){
                hash[s.charAt(l)-'a']--;
                l++;
            }
            maxlen = Math.max(maxlen,r - l + 1);
        }
        return maxlen;
    }
}