Hashing-1 Solved

Problem1.java

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+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+//https://leetcode.com/problems/group-anagrams/
+//Time Complexity O(N)
+//Space Complexity O(N)
+
+public class Problem1 {
+    public List<List<String>> groupAnagrams(String[] strs) {
+
+        Map<Double, List<String>> anagrams = new HashMap<>();
+
+        for(String str :strs){
+
+            Double hashVal = getHash(str);
+            List<String> anaList = anagrams.getOrDefault(hashVal, new ArrayList<>());
+            anaList.add(str);
+            anagrams.put(hashVal,anaList);
+
+        }
+
+        return new ArrayList<>(anagrams.values());
+    }
+
+
+    Double getHash(String input){
+        int[] primeArray = new int[] {2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101};
+        double hash = 1;
+        char[] inputChars = input.toCharArray();
+        for(char c : inputChars){
+            hash = hash * primeArray[c-'a'];
+        }
+
+        return hash;
+
+    }
+}

Problem2.java

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+import java.util.HashMap;
+
+//https://leetcode.com/problems/isomorphic-strings/
+//Time complexity O(N)
+//Space complexity O(1) as space could not be more than the character set
+public class Problem2 {
+    public boolean isIsomorphic(String s, String t) {
+
+        if(s.length() != t.length()){
+            return false;
+        }
+        HashMap<Character,Character> st1 = new HashMap<>();
+        HashMap<Character,Character> st2 = new HashMap<>();
+
+        for(int i=0;i<s.length();i++){
+            char sc = s.charAt(i);
+            char tc = t.charAt(i);
+            if(!st1.containsKey(sc)){
+                st1.put(sc,tc);
+            }else{
+                if(!st1.get(sc).equals(tc)){
+                    return false;
+                }
+            }
+            if(!st2.containsKey(tc)){
+                st2.put(tc,sc);
+            }else{
+                if(!st2.get(tc).equals(sc)){
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+}

Problem3.java

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+import java.util.HashMap;
+import java.util.Map;
+
+//https://leetcode.com/problems/word-pattern/description/
+//Time complexity O(N)
+//Space complexity O(N)
+public class Problem3 {
+    public boolean wordPattern(String pattern, String s) {
+        Map<Character,String> map = new HashMap<>();
+        Map<String,Character> strMap = new HashMap<>();
+        char[] patternChar = pattern.toCharArray();
+        String[] strArr = s.split(" ");
+        if(patternChar.length !=strArr.length ){
+            return false;
+        }
+        for(int i=0;i<patternChar.length;i++){
+            if(map.containsKey(patternChar[i])){
+                if(!map.get(patternChar[i]).equals(strArr[i])){
+                    return false;
+                }
+            }else{
+                map.put(patternChar[i],strArr[i]);
+
+
+            }
+
+
+            if(strMap.containsKey(strArr[i])){
+                if(!strMap.get(strArr[i]).equals(patternChar[i])){
+                    return false;
+                }
+            }else{
+                strMap.put(strArr[i],patternChar[i]);
+
+
+            }
+
+        }
+        return true;
+
+    }
+}