Complete Hashing-1

GroupAnagrams.java

@@ -0,0 +1,19 @@
+import java.util.*;
+
+// O(n*m) time, O(n) space;
+class Solution {
+    public List<List<String>> groupAnagrams(String[] strs) {
+        Map<String, List<String>> map = new HashMap<>();
+        for (String str : strs) {
+            int[] freq = new int[26];
+            for (char c : str.toCharArray()) {
+                freq[c - 'a']++;
+            }
+            String key = Arrays.toString(freq);
+            map.putIfAbsent(key, new ArrayList<>());
+
+            map.get(key).add(str);
+        }
+        return new ArrayList<>(map.values());
+    }
+}

IsomorphicStrings.java

@@ -0,0 +1,22 @@
+import java.util.*;
+
+// O(n) time, O(1) space since only 26 chars
+class Solution {
+    public boolean isIsomorphic(String s, String t) { 
+        Map<Character, Character> sMap = new HashMap<>();
+        Map<Character, Character> tMap = new HashMap<>();
+
+        for (int i = 0; i < s.length(); i++) {
+            char sChar = s.charAt(i);
+            char tChar = t.charAt(i);
+
+            sMap.putIfAbsent(sChar, tChar);
+            tMap.putIfAbsent(tChar, sChar);
+
+            if ((sMap.get(sChar) != tChar) || (tMap.get(tChar) != sChar)) {
+                return false;
+            }
+        }
+        return true;
+    }
+}

WordPattern.java

@@ -0,0 +1,27 @@
+import java.util.*;
+
+// O(n) time, O(n) space 
+
+class Solution {
+    public boolean wordPattern(String pattern, String s) {
+        String[] parts = s.split(" ");
+
+        if (parts.length != pattern.length()) return false;
+
+        Map<Character, String> charMap = new HashMap<>();
+        Map<String, Character> wordMap = new HashMap<>();
+
+        for (int i = 0; i < pattern.length(); i++) {
+            char c = pattern.charAt(i);
+            String word = parts[i];
+
+            charMap.putIfAbsent(c, word);
+            wordMap.putIfAbsent(word, c);
+
+            if ((!charMap.get(c).equals(word)) || (!wordMap.get(word).equals(c))) {
+                return false;
+            }
+        }
+        return true;
+    }  
+}