Done Hashing -1

Exercise1.java

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+class Solution {
+    //I use a HahMap where the key is stored in sorted version of each string and the value is list of anagrams.
+    //Since anagrams share identical sorted character sequences, sorting normalizes them into the same key.
+    //I group all original strings under their sorted key and return all grouped values
+    public List<List<String>> groupAnagrams(String[] strs) {
+       HashMap <String, List<String>> map = new HashMap<>();
+       for(String str : strs){
+        char[] sortedArr = str.toCharArray();
+        Arrays.sort(sortedArr);
+        String sortedStr = String.valueOf(sortedArr);
+        if(!map.containsKey(sortedStr)){
+            map.put(sortedStr, new ArrayList<>()); 
+        }
+        map.get(sortedStr).add(str);
+               }
+               return new ArrayList<>(map.values());
+    }
+}
+

Exercise2.java

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+class Solution {
+    // I use two hashmaps to maintain one-to-one mapping between characters s and t 
+    //for each index, i chek whether an existing mapping conflicts in either direction,if it does, return false
+    //If I finish loop without conflicts, the string are isomorphic, return true
+
+    public boolean isIsomorphic(String s, String t) {
+        HashMap<Character, Character> STmap = new HashMap<>();
+        HashMap<Character, Character> TSmap = new HashMap<>();
+        for(int i = 0; i < s.length(); i++){
+            char c1 = s.charAt(i);
+            char c2 = t.charAt(i);
+            if(STmap.containsKey(c1) && STmap.get(c1) != c2)
+            return false;
+            if(TSmap.containsKey(c2) && TSmap.get(c2) != c1)
+            return false;
+            STmap.put(c1, c2);
+            TSmap.put(c2,c1);
+
+        }   
+                 return true;
+
+         }
+}

Exercise3.java

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+class Solution {
+    // I split the string into words and checked if the pattern length matches the number of words.
+    // I used two hashmaps to maintain a bijetion - one mapaping pattern to words, other words to characters.
+    // while iterating, I return false if any existing mapping mismatchedl otherwise stored the mapping return true at the end.
+
+    public boolean wordPattern(String pattern, String s) {
+        String[]words = s.split(" ");
+        if(pattern.length() != words.length){
+            return false;
+        }
+        HashMap<Character, String> mapPT = new HashMap<>();
+        HashMap<String, Character>mapTP = new HashMap<>();
+        for (int i = 0; i < pattern.length(); i++){
+            char ch = pattern.charAt(i);
+            String word = words[i];
+            if(mapPT.containsKey(ch) && !mapPT.get(ch).equals(word)){
+                return false;
+
+            }  
+            if(mapTP.containsKey(word)&&!mapTP.get(word).equals(ch)) {
+                return false;
+            }   
+            mapPT.put(ch, word);
+            mapTP.put(word,ch);
+             }
+        return true;
+
+    }
+}