Added isomorphic string problem code

Author: Karnika06

Data Structures/Graphs/Negative_weight_cycle.cpp

@@ -0,0 +1,81 @@
+/* Implementation of Isomorphic Strings problem
+ * 
+ * In this problem, we will be given two strings s and t, we need to determine if they
+ * are isomorphic strings or not
+ * 
+ * Two strings s and t are isomorphic if the characters in s can be replaced to get t.
+
+ * All occurrences of a character must be replaced with another character while preserving 
+ * the order of characters. No two characters may map to the same character, but a character 
+ * may map to itself.
+ * 
+ * Problem link: https://leetcode.com/problems/isomorphic-strings/
+ * 
+ */
+
+import java.util.*;
+import java.io.*;
+
+class IsomorphicStrings
+{    
+    public boolean isIsomorphic(String s, String t) 
+    {
+         if(t.length() == s.length())
+         {
+             Map<Character, Character> sTMap = new HashMap<>();
+             Map<Character, Character> tSMap = new HashMap<>();
+             for(int i=0; i<t.length(); i++)
+             {
+                Character sChar = s.charAt(i);  
+                Character tChar = t.charAt(i);
+                 
+                 if(sTMap.containsKey(sChar))
+                 {
+                     if(sTMap.get(sChar)!=tChar)
+                        return false;
+                 }
+                 if(tSMap.containsKey(tChar))
+                 {
+                     if(tSMap.get(tChar)!=sChar)
+                        return false;
+                 }
+                 sTMap.put(sChar, tChar);
+                 tSMap.put(tChar, sChar);
+             }
+             return true;
+         }
+         //if s and t have different lengths they cannot be isomorphic
+         else 
+             return false;      
+        }
+        
+    public static void main()
+    {
+        Scanner sc = new Scanner(System.in);
+        String s = sc.next();
+        String t = sc.next();
+        IsomorphicStrings obj = new IsomorphicStrings();
+        System.out.println(obj.isIsomorphic(s,t));
+    }
+}
+
+/*
+Example 1:
+
+Input: s = "egg", t = "add"
+Output: true
+
+Example 2:
+
+Input: s = "foo", t = "bar"
+Output: false
+
+Example 3:
+
+Input: s = "paper", t = "title"
+Output: true
+
+Time Complexity: O(n)
+Space Complexity: O(n)
+
+*/